Polymeric ionic liquids, methods of making and methods of use thereof

ABSTRACT

Polymeric ionic liquids, methods of making and methods of using the same are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. Ser. No.13/058,088 filed Jun. 16, 2011, now allowed, which claims the benefit ofthe PCT/US2009/053319 filed Aug. 10, 2009, which also claims the benefitof the provisional patent application Ser. No. 61/087,411 filed Aug. 8,2008 which is also expressly incorporated herein, by reference, in itsentirety.

STATEMENT REGARDING SPONSORED RESEARCH

This invention was made with government support under National ScienceFoundation, Grant No. CHE-0748612. The government has certain rights inthis invention.

BACKGROUND OF THE INVENTION

There is no admission that the background art disclosed in this sectionlegally constitutes prior art. Solid phase microextraction (SPME) is apopular solvent-free sampling technique developed by Pawliszyn andco-workers in the early 1990s. SPME has gained widespread acceptance anduse in laboratories due to the fact that it is a solvent-less extractiontechnique, its mode of operation is relatively simple and easy toautomate, and sampling and sample preparation are combined into onesingle step.

SPME consists of a fiber that is coated with a stationary phasematerial, typically composed of a liquid polymer, solid sorbent, or amixture of both. Equilibrium is established between an analyte and thecoating material when the fiber is exposed to a solution, which allowsthe technique to be applied to both headspace and direct-immersionsampling. When SPME is coupled with gas chromatography (GC), theanalytes are desorbed from the fiber coating by thermal desorption inthe injection port of the GC.

The development of new coating materials for SPME has flourished in thepast decade as the technique continues to gain wide-spread popularity.The need for new coating materials is underscored by the fact that SPMEmethods must achieve high sensitivity and selectivity. The coatingmaterial must be designed to be resistant to extreme chemicalconditions, such as pH, salts, organic solvents, and modifiers.

To achieve long fiber lifetimes, the coating should be thermally stableto avoid excessive losses during the high temperature desorption step,while also maintaining physical integrity of the film.

As SPME methods become more developed in sampling complicatedenvironmental and biological matrices, structural tunability is adesirable means of modulating specific properties of the coatingmaterial while retaining others.

Further, a major challenge facing the world today is the development ofa sustainable civilization. An integral component to maintainingsustainability lies with the replacement of polluting processes bybenign or “green” alternatives. As industrial practices investigate newgreen processes, key variables such as cost, feasibility, andsignificance of improvements are all considerations that influence theadoption of any feasible process.

Description and Properties of Ionic Liquids (ILs)

Ionic liquids (ILs) are a class of compounds that can be tailorsynthesized to exhibit unique solvent properties while retaining manygreen characteristics. Despite widespread interest in ILs, therecontinue to be many properties of ILs that are not well-understood.Paramount of these properties is how the structures of the cationic andanionic moieties comprising the IL influence the partitioning behaviorof various molecules. No single study or collection of studies performedto this date can be used to conclusively predict or explain the role ofthe IL cation and/or anion on the observed partitioning behavior.

Ionic liquids (IL) and their polymerized analogs constitute a class ofnon-molecular, ionic solvents with low melting points. Also known asliquid organic, molten, or fused salts, most ILs possess melting pointslower than 100° C. Most widely studied ILs are comprised of bulky,asymmetric N-containing organic cations (e.g., imidazole, pyrrolidine,pyridine) in combination with any wide variety of anions, ranging fromsimple inorganic ions (e.g., halides) to more complex organic species(e.g., triflate).

ILs have negligible vapor pressures at room temperature, possess a widerange of viscosities, can be custom-synthesized to be miscible orimmiscible with water and organic solvents, often have high thermalstability, and are capable of undergoing multiple solvation interactionswith many types of molecules. The plethora of interaction capabilitiesILs are capable of undergoing include: hydrogen bond acidity, hydrogenbond basicity, π-π, dipolar, and dispersion interactions. Theseinteractions are directly related to the structures of thecationic/anionic moieties that comprise the IL.

The aforementioned properties have made molten organic salts andimidazolium and pyrrolidinium-based ILs an interesting and useful classof stationary phase materials in GC. In particular, it has been shownthat the separation selectivity and thermal stability can be altered bychanges to the cation and/or anion, polymerization and immobilization ofthe IL, and by blending different ILs to form stationary phases withvaried composition. While a series of reports have described the use ofILs in single drop microextraction (SDME) and liquid phasemicroextraction (LPME), only two reports have studied the use of ILs inSPME.

Liu and co-workers reported the development of a disposable IL coatingfor the headspace extraction of benzene, toluene, ethylbenzene, andxylenes. The resulting fibers possessed comparable recoveries to thecommercial fibers coated with polydimethylsiloxane (PDMS).

To allow for a better wetting and increased loading of the IL on thefused silica fiber, Hsieh and co-workers utilized a Nafion membranefollowed by dip coating of the SPME fiber in an IL. The fibers were usedto extract polycyclic aromatic hydrocarbons (PAHs) from aqueoussolution. Using GC-MS, detection limits of around 4-5 ng L⁻¹ wereobtained with relative standard deviations ranging from 6-12%. In bothof these reports, the IL had to be re-coated on the fiber after eachextraction and desorption step, which significantly reduces theconvenience and high-throughput nature inherent to SPME.

It has been observed that many classes of neat ILs have a strongpropensity to flow off the fiber when employing moderate to highdesorption temperatures (200° C. and above) and desorption times of 4minutes or longer. Several complications arise from the loss of the ILduring the desorption step: (1) a compromise between the desorption timeand temperature must be achieved; (2) due to the fact that the IL dripsinto the injection port and contaminates the liner, it must beconstantly removed and cleaned to prevent unwanted IL-decompositionproducts to appear as chromatographic ghost peaks; and, (3) the SPMEfiber needs to be re-coated with the IL, thereby making it inconvenientwhile also decreasing fiber-to-fiber reproducibility.

Due to the negligible vapor pressure inherent to ILs, ILs are not lostat high temperatures and may be recovered and re-used, demonstratingtheir potential as green solvents. In addition, the implementation ofprocesses using many classes of ILs may minimize the potential forexplosions due to the lack of flashpoint and reduced flammability ofmany ILs. Numerous reports have demonstrated enhanced reaction kineticsand favorable product ratios when performing various organic reactionsin an IL instead of traditional organic solvents.

Uses of Ionic Liquids in Analytical Extractions

The initial impetuses for the widespread interest in ILs were organicsynthesis and the growth of green chemistry. Research interest in ILshas extended into many fields of science involving an interdisciplinarygroup of researchers. The numbers of publications examining basicproperties and novel applications of ILs have increased over 850% from2000 to 2006. The study and applications involving ILs in analyticalchemistry has been lagging despite the vast opportunities offered bythese designer solvents.

In an attempt to better understand the solvation properties of ILs,prior studies have set out to compare the partitioning behavior ofneutral, amino-aromatic compounds, and compounds containing mixed acidicand basic functionality in octanol/water and ionic liquid/water systems.While the aforementioned compounds seemed to correlate well between thetwo systems, a considerable divergence was noted for acidic compounds aswell as a strong pH dependence on overall partitioning. Other studieshave explored the partitioning of metal ions by task-specific ILs, theuse of ILs as extraction media in deep desulfurization of diesel fuels,as well as the use of extractants to remove ions from aqueous solutions.

However, no single study or collection of studies can be used toconclusively predict or explain the role of the IL cation and/or anionon the observed partitioning behavior. Due to recent rapid advances inIL synthesis, it has been proposed that the extensive range of availablecations and anions could produce up to 10¹⁸ different ILs. Arelationship between the structure of ILs and their correspondingphysicochemical and solvation properties is desperately needed tointelligently design new classes of ILs for specific applications.

Task-Specific Ionic Liquids

The term “task-specific ionic liquids” (TSILs) relates to salts thatincorporate functional groups into one or both of the ions to impartspecific interactions with dissolved substrates; e.g., the use of urea,thiourea, and thioether functional groups to remove Hg²⁺ and Cd²⁺ fromaqueous solutions. In another example, the reactive capture of CO₂ wasdemonstrated by a TSIL containing a tethered amine group. The aminesequesters CO₂ through the formation of an ammonium carbamate complexwith the TSIL. While many of these elegant compounds have been studiedin synthetic reactions and in large scale extraction processes, therehas been little work that investigates the incorporation of thesecompounds into task-specific microextraction devices or applications inother areas of separation science.

Absorbent Coatings for Solid Phase Microextraction and Stir Bar SorptiveExtraction

Solid phase microextraction (SPME) and stir bar sorptive extraction(SBSE) are two solvent-free sampling techniques in which sampling andsample preparation are combined into one single step. SPME consists of afused silica fiber that is coated with an absorbent or adsorbent coatingmaterial, typically polydimethylsiloxane (PDMS), polyacrylate, orcarbowax divinylbenzene. Depending on the mode of extraction (headspaceor direct immersion), the analytes are sampled due to their partitioningto the coating material, typically under equilibrium conditions. Theanalytes are desorbed from the fiber using either thermal desorption(i.e., injection port of a gas chromatograph) or by solvent desorption(i.e., solvent chamber coupled to a high performance liquidchromatograph).

SBSE operates in a similar manner to SPME but differs in the type ofsupport and the amount of coating material employed in the extraction.In SBSE, the analytes are extracted into a thick polymer coating on amagnetic stir bar. The amount of coating material in SBSE is ˜50-250times larger than SPME, which produces a distinct sensitivityenhancement.

Polymer coating materials used in SBSE have largely focused on PDMS,although there has been a report of incorporating sol-gel technologyinto the PDMS coating material. The development of new coating materialsfor SPME has flourished in the past five years as the technique hasgained wide-spread popularity.

As described above, only two reports have studied the use of ILs inSPME. In both cases, several ILs were chosen and coated on the supportto carry out the extraction. Both reports indicated the extractionefficiencies obtained were superior to commercial SPME coatingmaterials. No reports have yet used IL-SPME for the determination ofanalyte partition coefficients. There have also been no studies reportedon the use of TSILs in SPME. Moreover, to the best of the inventors'knowledge, no SPME or SBSE coating material has yet been shown toeffectively extract nucleic acids, which has tremendous opportunity inall aspects of bioscience.

There is a need for new coating materials which is underscored by thefact that SPME methods must achieve high sensitivity and selectivity. Inaddition, the coating material must be designed to be resistant toextreme chemical conditions, such as pH, salts, organic solvents, andmodifiers. Additionally, the coating must be thermally stable tomaintain physical integrity during the lifetime of the fiber.

There is a further need for ILs that possess the ability to bestructurally tuned to effectively meet any physical or chemicalrequirements.

There is also a need for improved solvent-free sampling techniques. Inparticular, there is a need for improved the solid phase microextraction(SPME) methods.

SUMMARY OF THE INVENTION

The present invention is based, at least in part, on the inventors'discovery of the ion exchange mechanism occurring between IL-basedmaterials and aqueous solutions of nucleic acids. The inventors'discovery provides a fundamental understanding into the preferentialextraction of biomolecules. In addition, the inventors' discovery isespecially useful in the realm of ionic liquids and separation science,particularly in the areas of biology and biochemistry, and in thegeneral environmentally sustainable areas.

In a first broad aspect, there is provided herein a polymeric ionicliquid (PIL) comprising: i) a cationic component comprised of an ionicliquid (IL) that is polymerized, and ii) one or more anionic components,wherein the anionic components can be the same or different.

In another broad aspect, there is provided herein a mixture comprisingone or more of: i) mixtures of PILs, ii) mixtures of PILs and neat ILs,iii) mixtures of PILs and at least one organic solvent, iv) mixtures ofPILs, ILs, and at least one organic solvent, iv) mixtures of PILs, ILs,at least one organic solvent, and at least one other polymeric system,including, but not limited to PDMS, PEG, PA, and silicone oils.

In certain embodiments, the cationic component comprises least one ormore: quaternary ammonium, protonated tertiary amine, thionium,phosphonium, arsonium, carboxylate, sulfate or sulfonate groups whichmay be substituted or unsubstituted, saturated or unsaturated, linear,branched, cyclic or aromatic.

In certain embodiments, the cationic component is described by thegeneral formula of (XRR′R″H)⁺, where X is N, P, or As, and where each ofR, R′, R″ is selected from the group consisting of proton, aliphaticgroup, cyclic group and aromatic group.

In certain embodiments, the cationic component is described by theformula of XR₄ ⁺, wherein R is proton, aliphatic group (e.g., propyl,butyl), cyclic group (e.g., cyclohexane) or aromatic group (e.g., vinyl,phenyl). For example, in certain embodiments, the R, R′ and R″ aredifferent from each other.

In certain embodiments, the cationic component comprises: a quaternaryammonium, a protonated tertiary amine, imidazolium (IM) or substitutedIM, pyrrolidinium or substituted pyrrolidinium, or pyridinium orsubstituted pyridinium.

In certain embodiments, wherein the cationic component includes one ormore amine functional groups within the cation.

In certain embodiments, the PIL is polymerized to form linear polymersand/or cross-linked using varying ratios ofmonocationic/dicationic/tricationic/multcationic crosslinking molecules.

In certain embodiments, the cationic component comprises one or more of:monocationic components, dicationic components, tricationic components,other multicationic components, and mixtures thereof.

In certain embodiments, the cationic component comprises an IL monomermodified through one or more of: incorporation of longer alkyl chains,aromatic components, and/or hydroxyl-functionality. Non-limitingexamples include where cationic component comprises one or more of:VHIM⁺; VDDIM⁺, VHDIM⁺, BBIM⁺,

In addition, other non-limiting examples include where the PIL includesone or more of: poly(VHIM⁺ NTf₂ ⁻); poly(VDDIM⁺ NTf₂ ⁻), poly(VHDIM⁺NTf₂ ⁻), poly(BBIM⁺ NTf₂ ⁻), poly(BBIM⁺ taurate⁻), poly(BBIM⁺ A⁻).

In another broad aspect, there is provided herein a method for preparinga polymeric ionic liquid (PIL), comprising reacting an ionic liquidmonomer (IL) with RX to form a polymer, and using a metathesis anionexchange used to exchange the halide anion with a counter anion.

In certain embodiments, the PIL can be synthesized by free radicalpolymerization. In other embodiments, the PIL can be synthesized by apolymerization reaction involving one or more functional group attachedto an aromatic ring of the cationic component. Non-limiting examplesinclude where the polymerization reaction includes one or more of:cationic and anionic chain growth polymerization reactions,Ziegler-Natta catalytic polymerization, and step-reactionpolymerization; use of two different monomers to form copolymers throughaddition and/or block copolymerization.

In another non-limiting example, the PIL can be synthesized using acondensation polymerization to connect through functional groups such asamines and alcohols. In another example, the PIL can be synthesizedusing a cross-linking reaction.

In a specific example, the PIL can be synthesized by free radicalpolymerization of an imidazolium salt. Non-limiting examples includewhere the PIL is synthesized by free radical polymerization of one ormore of: 1-vinyl-3-hexylimidazolium chloride,1-vinyl-3-dodecylimidazolium bromide, and 1-vinyl-3-hexadecylimidazoliumbromide.

In certain embodiments, the anionic group comprises one or more of:carboxylate, sulfate or sulfonate groups which may be substituted orunsubstituted, saturated or unsaturated, linear, branched, cyclic oraromatic.

In certain embodiments, the anionic group comprises an amino acidcomponent, bis[(trifluoromethyl)sulfonyl]imide, or any anion containingi) fluorine groups and ii) primary, secondary, or tertiary amine groups.In a specific example, the anionic group comprises a taurate component.

In certain embodiments, the PILs have a solid/liquid transitiontemperature of about 400° C. or less.

In certain embodiments, the anionic component is exchanged throughbiphasic anion metathesis with one or more of the cationic components.

In another broad aspect, there is provided herein a solvent comprising:at least one PIL and having a solid/liquid transition temperature isabout 400° C. or less and having a liquid range of about 200° C. ormore.

In another broad aspect, there is provided herein a device useful inchemical separation or analysis comprising: a support and at least onePIL adsorbed, absorbed or immobilized thereon.

In another broad aspect, there is provided herein a device comprisingone or more PILs functionalized to: (1) selectively extract one or moreanalytes of interest and to allow all other analytes to be removed sothat one or more pre-concentrated analytes can be separated, identifiedand/or quantified; and/or (2) to selectively extract all other moleculesso that the analyte(s) of interest can be removed from other moleculesthereby allowing them to be separated, identified, and/or quantified.

In another broad aspect, there is provided herein a device comprisingcoated or immobilized polymeric ionic liquids for solid phasemicroextraction (SPME), wherein one or more PILs are used in neatpolymeric form, or mixed with other ionic liquids or polymeric ionicliquids, solvents, other polymers, including but not limited to PDMS,PEG, silicone oils, or other chromatographic adsorbent materials.

In another broad aspect, there is provided herein a device comprisingone or more PILs chemically adsorbed onto a fiber support or chemicallyattached by use of any chemical reaction mechanism.

In another broad aspect, there is provided herein a separation devicecomprising a support at least partially coated with one or more PILs.

In another broad aspect, there is provided herein a use of theseparation device in one or more of: headspace extraction,direct-immersion extraction, or membrane protected SPME extraction.

One non-limiting example includes where the separation device can becoupled to gas chromatography (GC) in which one or more analytes arethermally desorbed in a GC injection port.

Another non-limiting example includes where the separation device can becoupled to HPLC in which a HPLC mobile phase or buffered component isused to desorb molecules from the support.

Another non-limiting example includes where the separation device can becoupled to capillary electrophoresis (CE) in which a running buffer fromthe CE is used to remove analytes from the support.

Another non-limiting example includes where one or more analytes to beseparated can exist in any forms of matter (solids, liquids, and gases)and can be of any chemical component (small molecules, ions, syntheticor natural polymers, macromolecules, biomolecules).

Another non-limiting example includes where the separation device can beused for applications in Liquid-phase microextraction and single dropmicroextraction.

Non-limiting examples include one or more of the following: the solidsupport is packed in a chromatographic column; the solid support is acapillary column useful in gas chromatography; the device is used insolid phase microextraction (SPME).

In another broad aspect, there is provided herein a device comprising anionic liquid (IL) polymerized on a surface of a solid support. Incertain embodiments, the polymerized ionic liquid (PIL) is adaptable todesorption after exposure to one or more analytes.

In certain embodiments, the IL is polymerized by reaction of at leastone free silanol group on the surface of a fused silica support with atleast one vinyl-terminated organoalkoxysilane. In other embodiments, theIL comprises one or more of: vinyl-substituted IL monomers and/orcrosslinkers, coated on the support with an initiator and heated toinduce free radical polymerization. In a particular embodiment, whereinthe initiator comprises 2,2′-azo-bis(isobutyronitrile) (AIBN).

In certain embodiments, the degree of crosslinking is modified tocontrol the consistency of the formed polymer with lower degrees ofcrosslinking resulting in a gel-like material. Also, in certainembodiments, the degree of crosslinking is modified to control theconsistency of the formed polymer with greater degrees of crosslinkingresulting in a more rigid, plastic-like coating. In other embodiments,the degree of crosslinking is modified to influence one or more of:mechanism of partitioning, including adsorption versus absorption, andoverall selectivity for targeted analyte molecules.

Also provided herein is a device configured for thermally desorbinganalytes from the support. In certain embodiments, the device comprisesa solvent desorption device coupled to a high performance liquidchromatography column (HPLC).

In another broad aspect, there is provided herein a separation devicecomprising an absorbent or absorbent coating comprised of at least onepolymeric ionic liquid (PIL) coated onto a support.

In certain embodiments, the separation device can comprise one or moreof the following: a stationary phase coating on the support; astationary phase coating coatings for useful for microextractions; acoating for solid phase microextraction (SPME); a support comprising oneor more of: a solid fused silica support, a stir bar, a fiber, a film, amembrane, a fibrous mat, a woven or non-woven material.

In another broad aspect, there is provided herein a method comprisingmixing one or more PILs with one or more solvents to vary the viscosityand surface tension of the PIL. In certain embodiments, the method canfurther include allowing the PIL to be suspended from a microsyringeconfigured for sampling of one or more analyte.

In certain embodiments, at least one suspended drop is used to sample ananalyte matrix (liquid, solid, or gas) and wherein the PIL is directlyinjected into a GC, HPLC, or CE or mixed with a solvent and thendirectly injected into GC, HPLC, or CE.

In certain embodiments, the analytes to be separated can exist in anyforms of matter (solids, liquids, and gases) and can be of any chemicalcomponent, including, but not limited to small molecules, ions,synthetic or natural polymers, macromolecules, biomolecules.

In another broad aspect, there is provided herein a use of at least oneIL and/or PIL in an extraction process.

In another broad aspect, there is provided herein a method for forming asolvent immiscible IL using an in-situ metathesis reaction.

In another broad aspect, there is provided herein a device for selectiveCO₂ absorbance, comprising at least one PIL on a support.

In another broad aspect, there is provided herein a device forsequestration of CO₂, comprising at least one PIL on a support.

In another broad aspect, there is provided herein a process of CO₂capture, comprising using at least one PIL as described herein.

In certain embodiments, the process can include being reversible byheating the PIL to temperatures around 70-110° C.

In another broad aspect, there is provided herein a device comprising atleast one PIL on a support, and capable of an on-support metathesisexchange of anions from an immobilized PIL absorbent material.

In certain embodiments, the PIL is at least partially crosslinked toallow swelling of the PIL for complete metathesis exchange.

In another broad aspect, there is provided herein a device forextraction of one or more of DNA, RNA, protein, nucleic acids, peptides,amino acids, cellular extracts and portions thereof, comprising at leastone PIL on a support.

In another broad aspect, there is provided herein a carbon sequestrationmethod, comprising bringing at least one of a reactant gas mixtureincluding carbon dioxide contact with a polymerized ionic liquid (PIL)carbon sequestration catalyst at a temperature wherein a solid carbondeposit is formed at the surface of the PIL carbon sequestrationcatalyst.

In certain embodiments, the method can include use of one or more PILswhich comprise: i) a cationic component comprised of an ionic liquid(IL) that is polymerized, and ii) one or more anionic components,wherein the anionic components can be the same or different.

In a particular embodiment, the method further includes recapturingsequestered CO₂ and reusing the PIL carbon sequestration catalyst.

In another broad aspect, there is provided herein a method of separatingone chemical from a mixture of chemicals comprising the steps of:providing a mixture of at least one first and at least one secondchemical; exposing the mixture to at least one solid support includingat least one PIL adsorbed, absorbed or immobilized thereon; and,retaining at least a portion of the first chemical on the solid supportfor some period of time. This method can also include where the PILcomprises: i) a cationic component comprised of an ionic liquid (IL)that is polymerized, and ii) one or more anionic components, wherein theanionic components can be the same or different. In certain embodiments,the method further includes at least one IL liquid mixed with the PILand wherein the mixture is immobilized on the solid support.

In certain embodiments, the solid support is a column and furthercomprising and wherein the mixture is passed through the column suchthat elution of the first chemical is prevented or delayed. In certainembodiments, the column is a capillary.

In certain embodiments, the mixture is carried in a gaseous mobilephase.

In another broad aspect, there is provided herein a method for producingan absorbent material for solid phase microextraction, comprising:polymerizing one or more ionic liquid (IL) monomers to produce apolymeric ionic liquid (PIL) material, and forming at least a partialcoating of the PIL material on a support, wherein the PIL materialsubstantially resists large viscosity drops with elevated temperatures,and exhibits thermal stability.

In certain embodiments, the PIL material comprises two or more polymericionic liquids. Also, in certain embodiments, one or more ionic liquid(IL) monomers can be used to synthesize the PIL using a free radicalreaction.

In certain embodiments, the PIL material is capable of incorporatingsimultaneous solvation interactions, depending on the analytes beingextracted.

In certain embodiments, the structural design of the PIL is selected inorder to achieve high thermal stability.

In certain embodiments, the PIL comprises one or more of non-molecularionic solvents, the solvent being comprised of at least one asymmetriccation paired with at least one anion.

In certain embodiments, the method can further include tuning one ormore of chemical and physical properties of the PIL through one or moreof: i) choice of the anion, and ii) modification of the cationstructure. Non-limiting examples include: where the cation comprises oneor more of: imidazolium-based monomers including functionalizedimidazolium, pyridinium, triazolium, pyrrolidinium, ammonium. Othernon-limiting examples include where the anion comprises one or more of:Cl⁻, Br⁻, I⁻, bis[(trifluoromethyl)sulfonyl]imide, PF₆ ⁻, BF₄ ⁻, CN⁻,SCN⁻, taurate, and/or other amino acid groups.

In certain embodiments, the PIL is substantially free of residualhalides following anion metathesis.

In certain embodiments, the PIL comprises one or more of:1-vinyl-3-hexylimidazolium chloride; 1-vinyl-3dodecylimidazoliumbromide, and 1-vinyl-3-hexadecylimidazolium bromide.

In certain embodiments, the method can further include forming a mixtureof PIL and one or more extraction additives or phase modifiers that aidin selectively increasing extraction efficiency or promoting wetting ofglass or metal substrates.

In certain embodiments, the extraction additives or phase modifierscomprise one or more of: micelles, monomer surfactants, cyclodextrins,nanoparticles, synthetic macrocycles, or other polymer aggregates.

In certain embodiments, the support comprises one or more of: fibers atleast partially coated with at least one PIL; stir bar supports; wallsof fused silica capillaries; small inner diameter fused silica supports.

In another broad aspect, there is provided herein a stationary phasemicroextraction material (SPME) for solid phase microextractioncomprising one or more poly ionic liquids (PILs). In certainembodiments, the solid phase microextraction material can furtherinclude one or more of: a support at least partially coated with thepolymeric ionic liquid; fibers at least partially coated with thepolymeric ionic liquid; fibers that comprise small inner diameter fusedsilica fibers.

In certain embodiments, the solid phase microextraction material caninclude ionic liquids that are comprised of one or more of non-molecularionic solvents comprised of bulky, asymmetric cations paired with one ormore types of anions. In certain embodiments, one or more of chemicaland physical properties of the PILs are capable of being tunable throughchoice of anion and/or modification of the cation structure.

In certain embodiments, the PIL coating material includes one or moreextraction additives or phase modifiers that aid in selectivelyincreasing the extraction efficiency or promoting wetting of glass ormetal substrates. In certain embodiments, the extraction additives orphase modifiers comprise one or more of: micelles, monomer surfactants,cyclodextrins, nanoparticles, synthetic macrocycles, or other polymeraggregates.

In another broad aspect, there is provided herein a method forextraction of one or more samples, wherein the samples are solid,liquid, or gas comprising using a solid phase microextraction (SPME)material comprising one or more polymeric ionic liquids (PILs). Incertain embodiments, the SPME material is capable of use in remote fieldanalysis.

In certain embodiments, the solid phase microextraction material isamenable to hyphenation with gas chromatography (GC).

In another broad aspect, there is provided herein a method for producingan absorbent material for solid phase microextraction (SPME),comprising: polymerizing one or more ionic liquid monomers to produce apolymeric ionic liquid (PIL) absorbent material, and forming at least apartial coating of the PIL absorbent material on a support, wherein thePIL absorbent material resists large viscosity drops with elevatedtemperatures, and exhibits thermal stability. In certain embodiments,the PIL comprises two or more PILs. Also, in certain embodiments, one ormore PILs are synthesized by a free radical reaction. In certainembodiments, the PIL absorbent material comprises one or more ofnon-molecular ionic solvents comprised of bulky, asymmetric cationspaired with at least one type of anion.

In certain embodiments, the method can further include tuning one ormore of chemical and physical properties of the PIL through the choiceof anion and/or modification of cation structure. In certainembodiments, the PIL absorbent material is capable of incorporatingsimultaneous solvation interactions, depending on the analytes beingextracted. Also, in certain embodiments, the structural design of thePIL is selected in order to achieve high thermal stability. Inparticular embodiments, the PIL is substantially free of residualhalides following anion metathesis. Non-limiting examples include wherebis[(trifluoromethyl)sulfonyl]imide salts paired with large, bulkycations are used to produce PILs with thermal stability.

Other non-limiting examples include where the PIL comprise one or moreof: imidazolium-based monomers including functionalized imidazolium,pyridinium, triazolium, pyrrolidinium, ammonium cations with anionsincluding Cl⁻, Br⁻, I⁻, bis[(trifluoromethyl)sulfonyl]imide, PF₆ ⁻, BF₄⁻, CN⁻, SCN⁻, taurate and/or amino acids.

In certain embodiments, the desorption temperature and desorption timeare optimized to prolong the lifetime of the absorbent material.

In certain embodiments, the polymeric ionic liquids comprise one or moreof: 1-vinyl-3-hexylimidazolium chloride; 1-vinyl-3-dodecylimidazoliumbromide, and 1-vinyl-3-hexadecylimidazolium bromide.

In certain embodiments, the PIL absorbent material includes one or moreextraction additives or phase modifiers that aid in selectivelyincreasing the extraction efficiency or promoting wetting of glass ormetal substrates.

In certain embodiments, the extraction additives or phase modifierscomprise one or more of: micelles, monomer surfactants, cyclodextrins,nanoparticles, synthetic macrocycles, or other polymer aggregates.

In certain embodiments, the support comprises one or more: fibers atleast partially coated with the PIL material; stir bar supports; wallsof fused silica capillaries; small inner diameter fused silica supports.

In certain embodiments, the polymeric ionic liquids comprise one or moreof: 1-vinyl-3-hexylimidazolium chloride; 1-vinyl-3-dodecylimidazoliumbromide, and 1-vinyl-3-hexadecylimidazolium bromide.

In certain embodiments, the solid phase microextraction material isamenable to hyphenation with high performance liquid chromatography(HPLC).

In another broad aspect, there is provided herein a use of PILs indeveloping one or more task-specific ionic liquids (TSILs) ofmicroextraction coatings, chromatographic media, membrane systems, andchemical sensors.

In another broad aspect, there is provided herein a process forpolymerizing an ionic liquid (IL), comprising: i) attaching a vinyl (orallyl) functional group on a ionic liquid molecule; and ii) transformingthe composition of step i) into a polymer in which the unit ofunsaturation is gone, thereby forming a linear polymer.

In another broad aspect, there is provided herein a process forpolymerizing an ionic liquid salt comprising using one or more of:living polymerization, condensation polymerization, addition of at leastone crosslinker to an IL monomer solution to form crosslinked orbranched-type polymers.

In one aspect, there is described herein, the incorporation of ionicliquids (ILs) and/or polymeric ionic liquid (PILs) materials intoanalytical microextractions. Such incorporation allows for thedetermination of analyte partition coefficients between these materialsand other solvents, as well as, provides for the development of new,highly tunable absorbent coatings.

Described herein is the use of polymeric ionic liquids (PIL) as a novelclass of stationary phase coatings for solid phase microextraction. Thepolymerization of IL monomers produces materials that can be coated asthin films on supports, while resisting large viscosity drops withelevated temperatures and exhibiting exceptional thermal stability.

The long lifetime and high thermal stability of the PIL-based SPMEcoatings may provide them particular advantages in GC-MS applicationsinvolving highly selective ester and FAME extractions from complexmatrices.

Among the advantages of the present method are: fast, solvent-freeextraction and one step extraction; the concentration of analytes makeSPME time efficient; the samples can be solid, liquid, or gas; thecompact and portable nature of SPME allows for remote field analysis;and, the method is amenable to hyphenation with gas chromatography (GC)and high performance liquid chromatography (HPLC).

The structure of the IL monomer can be custom designed to incorporate amultitude of simultaneous solvation interactions depending on theanalytes being extracted and the complexity of the matrix.

In addition, the ILs described herein possess high thermal stabilitiesthereby limiting the bleed of the phase during the desorption step athigh GC injection port temperatures.

The highly tunable structure of the ILs described herein provides variedsolvation properties allowing for the development of highly selectivecoatings.

The highly selective IL-based absorbent coatings described hereinprovide opportunities for task-specific microextractions possessing lowdetection limits. In addition, the lifetime of IL-based coatingsdescribed herein is favorably comparable to commercial coatings.

In another aspect, there is provided a novel use of polymeric ionicliquids (PILs) which can be generally described herein as non-molecularionic solvents comprised of bulky, asymmetric cations paired withvarious anions. The chemical and physical properties of the PILsdescribed herein are highly tunable through the choice of anion andmodification of the cation structure.

In another broad aspect, there is provided herein a method of using ILsas absorbent coatings in solid phase microextraction (SPME). Inparticular, there are provided herein PILs that are useful as selectivecoatings for solid phase microextraction and for stir bar sorptiveextraction.

In another aspect, there is provided herein the use of PILs as selectivecoatings for the extraction of such analytes as esters using solid phasemicroextraction.

In a particular aspect, the inventors herein now show that bypolymerizing IL monomers to form polymeric ionic liquids (PILs), stableabsorbent coatings are developed for the analysis of esters in red andwhite wines as well as for the extraction of benzene, toluene, ethylbenzene, and xylenes in gasoline.

The IL monomers and their polymeric analogs (PILs) described hereinpossess many unique properties and characteristics that make themparticularly suitable as absorbent coatings for SPME. In onenon-limiting example, PILs can be coupled with GC for the development ofextraction methods for the analysis of such analytes as, for example,esters in red and white wines, as well as benzenes, toluenes, ethylbenzenes and xylenes (BTEX) compounds in gasoline.

The methods described herein exhibit good analyte recovery, linearityover a wide range of concentrations, high reproducibility, and goodsensitivity. In addition, the sensitivity can be further enhancedthrough the use of smaller inner diameter fused silica supports allowingfor thicker coatings.

These absorbent coatings have particular advantages in GC-MSapplications due to the fact that PIL coatings exhibit long lifetimes,low levels of thermal bleed, and high selectivity.

Various objects and advantages of this invention will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Illustrates the effect of the cation and anion on the surfacetension for dicationic ionic liquids.

FIG. 2: Illustrates the effect of the cation and anion on the densityfor dicationic ionic liquids.

FIG. 3: is a thermal stability diagram showing thedecomposition/volatilization of thin films coated on the walls of fusedsilica capillaries, heated under a constant flow of helium, using anultra-sensitive flame ionization detector. The plot illustrates the factthat the geminal dicationic ionic liquids (D-G) have much higher thermalstabilities, and/or lower volatilities, than conventional ionic liquids(A-C). A, 1-butyl-3-methylimidazolium chloride (BMIM-Cl); B, BMIM-PF₆;C, BMIM-NTf₂; D, C₉(bpy)₂-NTf₂, 38; E, C₉(mim)₂-NTf₂, 10; F,C₁₂(benzim)₂-NTf₂, 29; G, C₉(mpy)₂-NTf₂, 35.

FIG. 4: is a positive ion electrospray mass spectrum of mixture 4indicating the relative abundance of the three substituted dications aswell as the loss of a proton on the imidazolium ring thereby allowingthe formation of the +1 ion.

FIG. 5: is a plot illustrating the effect of 1-hexyl-3-vinylimidazoliumbis[(trifluoromethane)sulfonyl]imidate film thickness on the peakefficiency (theoretical plates/meter) of naphthalene at 100° C.

FIG. 6: is a chromatogram showing the separation of fatty acid methylesters (C₆-C₂₄) on a 15 meter partially cross-linked ionic liquidstationary phase (0.10% nvim-NTf₂ (2)/10% C₉(vim)₂-NTf₂ (5) with 7.5%AIBN). Conditions: 100° C. hold 2 minutes, 15° C./min to 260° C.

FIG. 7: A chromatogram showing the Separation of PAH and chlorinatedpesticide mixture on a 13 meter C₉(vim)₂-NTf₂ (7.5% AIBN) more likelycross-linked ionic liquid stationary phase. 1, indene; 2, naphthalene;3, biphenyl; 4, azulene; 5, acenaphthene; 6, acenaphthylene; 7,heptachlor; 8, fluorene; 9, BHC; 10, dibenzothiophene; 11, DDE; 12;endosulfan; 13, anthracene; 14, dieldrin; 15,4H-cyclopenta[def]phenanthrene; 16, fluoranthene; 17, DDT; 18, lindane;19, pyrene; 20, carbazole. Conditions: 175° C. for 1 min; 20° C./min to335° C. The smaller, unnumbered peaks in this chromatogram areimpurities contained in numbered standard materials.

FIG. 8: A syringe useful for SPME and SPME/MALDI mass spectrometry.

FIG. 9: Another syringe useful for SPME and SPME/MALDI massspectrometry.

FIG. 10 and FIG. 11 Schemes demonstrating the synthesis of the polymericionic liquids evaluated:

FIG. 10: The vinyl-substituted ionic liquid (IL) monomer is prepared bythe reaction of 1-vinylimidazole with the corresponding halo alkanefollowed by free radical polymerization to form the linear polymer.

FIG. 11: Metathesis anion exchange is used to exchange the halide anionwith the NTf⁻ anion.

FIG. 12: 1H-NMR spectra of the 1-dodecyl-3-vinylimidazolium bromide ILmonomer (top) and the corresponding polymeric ionic liquid followingfree radical polymerization (bottom).

FIGS. 13A-13D: Scanning electron micrographs of a 100 μm inner diameterbare fused silica support (FIG. 13A) and various angles of the fusedsilica support coated with the poly(ViDDIm⁺ NTf⁻) PIL (FIG. 13B), (FIG.13C), and (FIG. 13D). The estimated film thickness is approximately12-18 μm.

FIGS. 14A-14B: Sorption time profiles obtained for the poly(ViHIm⁺ NTf⁻)PIL fiber by extracting the studied analytes at a concentration of 200L⁻¹ at varying extraction time intervals using a constant stir rate of900 rpm at 23° C.:

FIG. 14A: (+) methyl nonanoate, (●) hexyl butyrate, (▪) methylcaprylate, (x) methyl enanthate, (▴) methyl caproate.

FIG. 14B: (□) methyl laurate, (Δ) methyl undecanoate, (⋄) methyldecanoate, (-x-) hexyl tiglate, (-●-) furfuryl octanoate, (-+-) benzylbutyrate.

FIG. 15: Gas chromatogram obtained following the headspace extraction ofa red wine sample spiked with 400 L⁻¹ of esters using a poly(ViDDIm⁺NTf2⁻) PIL fiber under optimal extraction conditions. 1. isopropylbutyrate, 2. ethyl valerate, 3. methyl caproate, 4. methyl enanthate, 5.methyl caprylate, 6. hexyl butyrate, 7. methyl nonanoate, 8. methyldecanoate, 9. hexyl tiglate, 10. benzyl butyrate, 11. methylundecanoate, 12. methyl laurate, 13. furfuryl octanoate.

FIG. 16: A schematic illustration showing a system for headspaceextraction.

FIGS. 17A-17D: Graphs showing the quantitative analysis of esters andfatty acid methyl esters in red and white wines: FIGS. 17A-17C: Thecalibration curves of 100 μm I.D. solid phase microextraction (SPME)fibers. FIG. 17D: The calibration curve of 50 μm I.D. SPME fiber.

FIG. 18: Chart showing figures of merit for PIL-based extractions inwine.

FIGS. 19A-19C: Graphs showing the quantitative analysis of BTEXcompounds in gasoline: FIG. 19A: The sorption time profile. FIG. 19B:The calibration curves.

FIG. 19C: The gas chromatogram of BTEX in gasoline.

FIG. 20: Chart showing the figures of merit for C16 PIL-based extractionin gasoline.

FIG. 21: Table 1 showing the correlation coefficient, sensitivity, anddetection limit of esters and fatty acid methyl esters (FAMEs) inMilli-Q water extracted by headspace sampling using three PIL coatedfibers.

FIG. 22: Table 2 showing the correlation coefficient, sensitivity, anddetection limit of esters and FAMEs in Milli-Q water extracted byheadspace sampling using three commercial fibers.

FIG. 23: Table 3 showing the figures of merit of calibration curvesobtained for three PIL coated fibers in a synthetic wine solution.

FIG. 24: Table 4 showing the figures of merit of calibration curvesobtained for two commercial fibers in a synthetic wine solution.

FIG. 25: Table 5 showing the recovery and reproducibility results foresters and FAMEs extracted from red wine at two calibration levels.

FIG. 26: Table 6 showing the recovery and reproducibility results foresters and FAMEs extracted from white wine at two calibration levels.

FIGS. 27A and 27B: Optical microscope photographs showing IL coatedfused silica fiber tip (FIG. 27A) and magnified portion (˜2.2 mm) of thesupport body (FIG. 27B).

FIG. 28: GC separation of 27 analytes extracted from the headspace suinga homemade SPME apparatus consisting of the IL polymer coating. Analytes1, 2, 8, 13, 14, 20 are small chained esters. 4, 6, 9, 11, 15, 18, 22are aliphatic hydrocarbons. 3, 5, 7, 10, 12, 16, 19 are fatty acidmethyl esters. 17, 21, 23-27 are phthalate esters. Conditions: 30 minextraction time; 600 μL, aqueous solution with 700 ppb of each analyte;˜400 μL headspace volume; desorption tem: 250° C.; desorption time: 4min.

FIG. 29: Table 7 showing the correlation coefficient sensitivity, anddetection limit of esters and FAMEs extracted by headspace samplingusing a polymerized ionic liquid absorbent coating. Each calibrationcurve was constructed using a minimum of 10 different concentrationlevels.

FIGS. 30A, 30B, 30: Structures of ionic liquids for creating coated(FIG. 30A) and immobilized (FIG. 30B, FIG. 30C) thin layers on solidsupports.

FIG. 31: Schematic illustration representing the coating and subsequentfree radical reaction to form a thin, immobilized/crosslinked IP layeron a 1 cm segment of fused silica.

FIGS. 32A-32B: Schematic illustration showing the formation of a thick(1.0 mm) (FIG. 32A) immobilized or crosslinked and (FIG. 32 B) coatedionic liquid layer on a glass stir bar support.

FIGS. 33A and 33B: Schematic illustration showing partitioningequilibria for an analyte (A) molecule in aqueous solution (S),headspace (H) and IL coated/immobilized on a solid support (IL): FIG.33A: A system in which the IL is coated/immobilized on a fused silicasupport. FIG. 33B: A system using a glass stir bar support.

FIGS. 34A-34C: Structures of various task-specific ionic liquids(TSILs).

FIG. 35: Schematic illustration of on-fiber metathesis anion exchangeusing a partially crosslinked IL coating. The Cl⁻ anions (left) arebeing exchanged and replaced by PB₆ ⁻ (right).

FIG. 36: Structure of -1butyl-3-butylimidazolium taurate (BBIM-taurate).

FIG. 37: Synthesis of BBIM-taurate.

FIG. 38: The gas chromatogram of BBIM-taurate.

FIG. 39: Photograph showing BBIM-taurate before (right) and after (left)CO₂ exposure.

FIG. 40: Chart showing sorption data of BBIM-taurate (⋄) and BBIM-NTf₂(□).

FIG. 41: Graph showing mole fraction and pressure for BBIM-taurate andBBIM-NTf₂

FIG. 42: Schemes demonstrating the synthesis of polymeric ionic liquidsused for capturing CO₂, including an example of synthesis oftaurate-based PIL.

FIG. 43: Apparatus of SPME setup for capture of CO₂.

FIG. 44: The gas chromatogram of a taurate-based IL.

FIG. 45: The gas chromatogram of the taurate-based PIL.

FIG. 46: Scanning electron micrograph of BBIM-taurate coated fiberbefore exposure to CO₂.

FIG. 47A and FIG. 47B: Scanning electron micrographs of BBIM-tauratecoated fiber after exposure to CO₂.

FIG. 48: Scanning electron micrograph of BBIM-taurate coated fiber afterdesorption.

FIG. 49: Sorption-time profile obtained under low pressure of CO₂showing the comparison of different IL-based sorbent coatings to 2commercial-based coatings (Carboxen and PDMS). The film thickness of thetwo commercial coatings are approximately six to seven times that of theIL-based systems.

FIG. 50: Sorption-time profile obtained under high pressure of CO₂showing the comparison of different IL-based sorbent coatings to 2commercial-based coatings (Carboxen and PDMS). The film thickness of thetwo commercial coatings are approximately six to seven times that of theIL-based systems.

FIG. 51: Sorption-time profile of CO₂ under medium pressure using theC₆-taurate based ionic liquid polymer.

FIG. 52: Structures of the ILs and PIL used in the HS-SPME-GC method. IL(A) was used as high temperature solvent to solubilize the analytes inthe study. PIL (B) was used as a SPME sorbent coating. IL (C) was usedas a low bleed, highly selective stationary phase in GC.

FIG. 53: Schematic diagram demonstrating the use of [HMIM][FAP] as aheadspace solvent, the poly[ViHDIM][NTf₂] PIL as SPME sorbent coating,and the [C₁₂(BIM)₂][NTf₂] IL as a high stability GC stationary phase.The analytes are (1) tricosane, (2) hexacosane, (3) methylheneicosanoate, (4) methyl behenate, (5) triacontane, and (6) methyltetracosanoate.

FIG. 54: Sorption-time profiles obtained for the PIL fiberpoly[ViHDIM][NTf₂] when performing headspace extraction at 170±10° C.using a concentration of 25 mg of analyte per kg of [HMIM] [FAP] IL. Thestudied analytes are: (●) tricosane, (Δ) hexacosane, (*) methylheneicosanoate, (◯) methyl behenate, (▪) triacontane, and (□) methyltetracosanoate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

To overcome the aforementioned challenges while retaining the uniquesolvation characteristics of ILs, the inventors herein now describe thedevelopment of polymeric ionic liquids (PILs). The inventors herein havenow discovered that materials coated with such PILs do not need to berecoated after every extraction, possess exceptional thermal stability,highly reproducible extraction efficiencies, and long lifetimes.

In a broad aspect, there is provided herein a method for producingpolymeric ionic liquids (PILs) using a free radical reaction. In certainembodiments, the ionic liquids (ILs) comprise one or more ofnon-molecular ionic solvents comprised of bulky, asymmetric cationspaired with various anions.

In certain embodiments, the method further includes tuning one or moreof the chemical and physical properties of ILs and/or PILs through thechoice of anion and modification of the cation structure. The PILmaterials are capable of incorporating simultaneous solvationinteractions, depending on the analytes being extracted. Further, incertain embodiments, the structural design of the polymeric ionic liquidcan be selected in order to achieve high thermal stability.

In certain embodiments, the PIL is substantially free of residualhalides following anion metathesis.

In one example, bis[(trifluoromethyl)sulfonyl]imide salts paired withlarge, bulky cations are used to produce IL monomers with exceptionalthermal stability.

In another example, the PILs can be comprised of one or more of:imidazolium-based monomers including functionalized imidazolium,pyridinium, triazolium, pyrrolidinium, ammonium cations with anionsincluding, but not limited to: Cl—, Br—, I—,bis[(trifluoromethyl)sulfonyl]imide, PF6-, BF4-, CN—, SCN—. Further, incertain embodiments, the polymeric ionic liquids comprise one or moreof: 1-vinyl-3-hexylimidazolium chloride; 1-vinyl-3-dodecylimidazoliumbromide, and 1-vinyl-3-hexadecylimidazolium bromide.

Also provided herein is a method for producing an absorbent material forsolid phase microextraction (SPME) which generally includes polymerizingionic liquid monomers to produce an absorbent PIL material, and formingat least a partial coating of the absorbent PIL material on a support.The absorbent PIL material resists large viscosity drops with elevatedtemperatures, and exhibits thermal stability.

In certain embodiments, the IL and/or PIL absorbent coating materialincludes one or more extraction additives or phase modifiers that aid inselectively increasing the extraction efficiency or promoting wetting ofglass or metal substrates.

In certain embodiments, the IL and/or PIL absorbent coating material caninclude one or more of: micelles, monomer surfactants, cyclodextrins,nanoparticles, synthetic macrocycles, or other polymer aggregates asextraction additives or phase modifiers that aid in selectivelyincreasing the extraction efficiency or promoting wetting of glass ormetal substrates. Further, in certain embodiments, the desorptiontemperature and/or desorption time can be optimized to prolong thelifetime of the coating material.

In certain embodiments, the support comprises one or more fibers atleast partially coated with the PIL absorbent material. In certainembodiments, the support comprises one or more stir bar supports. Incertain embodiments, the support comprises one or more walls of fusedsilica capillaries. In certain embodiments, the support comprises smallinner diameter fused silica supports.

In another broad aspect, there is provided herein a method extraction ofone or more samples where the samples are solid, liquid, or gascomprising using the PIL SPME as described herein. For example, incertain embodiments, such PIL SPME materials are capable of use inremote field analysis. Also, in certain embodiments, the PIL SPMEmaterials are amenable to hyphenation with gas chromatography (GC).

The present invention is further defined in the following Examples, inwhich all parts and percentages are by weight and degrees are Celsius,unless otherwise stated. It should be understood that these Examples,while indicating preferred embodiments of the invention, are given byway of illustration only. From the above discussion and these Examples,one skilled in the art can ascertain the essential characteristics ofthis invention, and without departing from the spirit and scope thereof,can make various changes and modifications of the invention to adapt itto various usages and conditions. All publications, including patentsand non-patent literature, referred to in this specification areexpressly incorporated by reference herein.

Example A—Diionic Salts

A “diionic salt” or “DIS” is a salt formed between a dication asdescribed herein and a dianion or two anions or between a dianion asdescribed herein and a dication or two cations. This term is not meantto embrace a single species that has a +2 or −2 charge such as Mg⁺² orSO₄ ⁻². Rather it contemplates a single molecule with two discreetmono-ionic groups, usually separated by a bridging group. The two ionicspecies should be of the same charge. T hey may be different types ofgroups or the diionic liquid salts may be “geminal” which means bothionic groups are not only the same charge, but also the same structure.The counterions need not be identical either. In one embodiment, eitherthe diion or the salt forming species is chiral, having at least onestereogenic center. In such instances, the diionic liquid salts may beracemic (or in the case of diastereomers, each pair of enantiomers ispresent in equal amounts) or they may be optically enhanced. “Opticallyenhanced” in the case of enantiomers means that one enantiomer ispresent in an amount which is greater than the other. In the case ofdiastereomers, at least one pair of enantiomers is present in a ratio ofother than 1:1. Indeed, the diionic liquid salts may be “substantiallyoptically pure” in which one enantiomer or, if more than one stereogeniccenter is present, at least one of the pairs of enantiomers, is presentin an amount of at least about 90% relative to the other enantiomer. Thediionic liquid salts of the invention may also be optically pure, i.e.,at least about 98% of one enantiomer relative to the other. Usually, theterm diionic salt is used to describe a salt molecule, although, as thecontext suggests, it may be used synonymously with “diionic liquid”(“DIL”) and “diionic liquid salt” (DILS”). A “diionic liquid” or “DIL”in accordance with the present invention is a liquid comprised ofdiionic salts. Thus, sufficient DS molecules are present such that theyexist in liquid form at the temperatures indicated herein. This presumesthat a single DS molecule is not a liquid. A DL is either a dicationicionic liquid or a dianionic ionic liquid (a liquid comprising eitherdicationic salts or dianionic salts as described herein). A “dicationicionic liquid” (used synonymously with “liquid salts of a dication”) inaccordance with the present invention is a liquid comprised of moleculeswhich are salts of dicationic species. The salt forming counter-anionsmay be mono-ionic such as, for example only, Br—, or dianionic, such as,again for example only, succinic acid. Any dicationic ionic liquid whichis stable and has a solid/liquid transformation temperature of 400° C.or less is contemplated. The same is true for “dianionic ionic liquids”also known as “liquid salts of a dianion,” except the charges arereversed. Dicationic liquids and dianionic liquids can also be referredto herein as diionic liquid salts (“DILS” or “DCLS” and “DALS” dependingupon charge).

Preferably, a dicationic ionic liquid or dianionic ionic liquid will notsubstantially decompose or volatilize (or remain substantiallynon-volatile) as measured by being immobilized as a thin film in a fusedsilica capillary or on a silica solid support as described herein, at atemperature of 200° C. or less. “Substantially” in this context meansless than about 10% by weight will decompose or volatilize at 200° C.inside a capillary over the course of about one hour. Moreover, thedicationic ionic liquid in accordance with this embodiment willpreferably have either a solid/liquid transformation temperature atabout 100° C. or less or a liquid range (the range of temperatures overwhich it is in a liquid form without burning or decomposing) of at least200° C.

In another embodiment, these dicationic ionic liquids will have both asolid/liquid transformation temperature at about 100° C. or less and aliquid range of at least 200° C.

In another aspect of the invention, a dicationic ionic liquid will notsubstantially volatilize or decompose, as discussed herein, at atemperature of less than about 300° C. “Substantially” in this contextmeans that less than about 10% by weight will decompose or volatilize at300° C. inside a capillary over the course of about one hour. Moreover,the dicationic ionic liquids in accordance with this embodiment willpreferably have either a solid/liquid transformation temperature at 25°C. or less. In another embodiment, the dicationic ionic liquids willalso have a liquid range of at least 200° C. In an even more preferredaspect of the invention, the liquid range will be 300° C. or above.

Preferably, a dianionic ionic liquid will not substantially decompose orvolatilize as measured by being immobilized as a thin film in a fusedsilica capillary as described herein, at a temperature of 200° C. orless. Moreover, the dianionic ionic liquid in accordance with thisembodiment will preferably have either a solid/liquid transformationtemperature at about 100 C or less or a liquid range of at least 200° C.

In another embodiment, these dianionic ionic liquids will have both asolid/liquid transformation temperature at about 100° C. or less and aliquid range (diionic molecule is stable over the entire temperaturerange) of at least 200° C.

In another aspect of the invention, a dianionic ionic liquid will notsubstantially volatilize or decompose, as discussed herein, at atemperature of less than about 300° C. Moreover, the dianionic ionicliquids in accordance with this embodiment will preferably have either asolid/liquid transformation temperature at about 25° C. or less. Inanother embodiment, the dianionic ionic liquids will also have a liquidrange of at least 200° C. In an even more preferred aspect of theinvention, the liquid range will be 300° C. or above.

Thus a diionic liquid in accordance with the present invention is eithera dicationic ionic liquid salt or a dianionic ionic liquid salt whichwill neither substantially decompose nor substantially volatilize, asmeasured as described herein, as a temperature of 200° C. or less andwill have a temperature of solid/liquid transformation temperature at100° C. or a liquid range of at least 200° C.

In other aspects of the invention, these diionic liquids will have bothsolid/liquid transformation temperature at about 100° C. or more and aliquid range of at least 200° C.

In other embodiments in accordance with the present invention, thediionic liquids, either dicationic ionic liquids or dianionic ionicliquids will be stable, that is not substantially volatilized ordecomposed, as discussed herein, at a temperature of less than about300° C. and will have a solid/liquid transformation temperature at about25° C. or less. A particular preferred embodiment of this aspect of thepresent invention, the diionic liquids will have a liquid range of atleast 200° C. and even more preferably at least 300° C. Any diioniccompound which can form a stable liquid salt that meets the broadestparameters is contemplated.

In another embodiment, the present invention provides a stable diionicliquid comprising at least one liquid salt of dianionic molecule ordicationic molecule of the structure of formula I or II: C-A-B-A′ (I) orC′-A-B-A′-C″ (II) wherein A and A′ are ether both anions or bothcations, or are both groups which overall have an anionic or cationiccharge and which may be the same or different, so long as they both havethe same charge (positive of negative); B is a bridging group (alsoreferred to as a chain or bridging moiety) that may be substituted orunsubstituted, saturated or unsaturated, aliphatic, including straightor branched chains, cyclic or aromatic, and which may contain, inaddition to carbon atoms and hydrogen, N, O, S and Si atoms; and C, C′and C″ are counter ions having a charge which is opposite that of A andA′. C′ and C″ are ether both mono-anionic or mono-cationic or groupswhich have a single anionic or cationic charge and may be the same ordifferent so long as they both have the same charge (positive ornegative) and C is ether dianionic or dicationic or contains two groupswhich each have a single anionic or cationic charge.

In another embodiment, A and A′ are cationic and are, withoutlimitation, substituted or unsubstituted, saturated or unsaturated,aliphatic including straight or branched chain, cyclic or aromatic,quaternary ammonium, protonated tertiary amine, phosphonium or arsoniumgroups. When A and A′ are cationic, C′ and C″ are anionic counterionswhich, without limitation, include halogens, mono-carboxylatesmono-sulfonates, mono-sulphates, NTf₂ ⁻, BF₄ ⁻, trifilates or PF₆ ⁻, andC is a dianionic molecule having two anionic groups each selected from,without limitation, carboxylate, sulfate or sulfonate groups. In anotherembodiment, A and A′ are anionic and are, without limitation,substituted or unsubstituted, saturated or unsaturated, aliphaticincluding straight or branched chain, cyclic or aromatic, carboxylates,sulfonates, and sulphates. When A and A′ anionic, C′ and C″ are cationiccounterions which, without limitation, include quaternary ammonium,protonated tertiary amine, phosphonium or arsonium groups. C is adicationic molecule which can be, without limitation, a compound havingtwo cationic groups each selected from quaternary ammonium, protonatedtertiary amine, phosphonium or arsonium groups. In another embodiment,these dianionic ionic liquids will have both a temperature ofsolid/liquid transformation of about 100° C. or less and a liquid rangeof at least 200.degree. C. In a particularly preferred embodiment, theseliquid salts of formula I or II have a solid/liquid transitiontemperature of from about 100° C. or less and/or a liquid range of 200°C. or more and/or are substantially non-volatile and non-decomposable attemperatures below 200° C.

Typically, the structural considerations for diionic liquids are thesame whether they are dianionic ionic liquids or dicationic ionicliquids. First, the diionic liquids will include a diionic species,either a dianionic or a dicationic molecule. The ionic species arenormally separated by a chain or bridging moiety or group as discussedherein. Any anion or cation which can provide a dianionic ionic liquidor dicationic ionic liquid is contemplated. These include those that areidentified above as A and A′. Possible cations include, withoutlimitation, quaternary ammonium (—N(R)₄)⁺, protonated tertiary amines(—N(R)₃H)⁺, phosphonium and arsonium groups. These groups can bealiphatic, cyclic, or aromatic. Examples of aliphatic ammonium dicationsare found in EXAMPLE A—Table 2 and examples aromatic ammonium dicationsare found in EXAMPLE A—Table 1. Anions may include, for example,carboxylates, sulphonates, or sulphonates. Examples of a dicarboxylicacid dianion include, without limitation, succinic acid, nonanedioicacid, and dodecanedioic acid. Other non-limiting examples of diionicspecies (dianions an dications including a generic bridging group)include:

The value of n is discussed in connection with the length of thebridging group. In addition, hybrid dianions and dications arecontemplated. Thus, for illustration only, a dication can be composed ofa quaternary ammonium group and an arsonium group and a dianion can becomposed of a carboxylate group and a sulphonate. The counter ions mayalso be different from each other.

The bridging group or chain interposed between the two ionic species canbe any length or any composition which affords a diionic liquid ofsuitable properties. These include the groups identified as B above.There are certain factors that should be considered in selecting such achain or bridging moiety. First, the larger the diionic molecule ingeneral, the greater the chance that the melting point or temperature ofsolid/liquid transformation will be elevated. This may be less of aconcern where the liquid range need not be extensive and the temperatureof solid/liquid transformation need not be terribly low. If, however,one desires a liquid range of about 200° C. or more and/or asolid/liquid transformation temperature at 100° C. or less, the size ofthe overall molecule can become a larger and larger factor. Second, thechain should have some flexibility. An excessive degree of unsaturatedgroups, the use of very rigid and/or stericly bulky groups can adverselyimpact the ability of the resulting materials to act as solvents andreduce their overall and utility. Thus, multiple fused ring structures,such as those found in, for example, cholesterol, and polyunsaturatedaliphatic groups with extensive unsaturation should generally beavoided.

In general, the length of the bridging group can range from a lengthequivalent to that of a saturated aliphatic carbon chain of betweenabout 2 and about 40 carbon atoms (e.g., n=C₂-C₄₀ when bridging group iscomposed of carbon). More preferably, the length should be approximatelythat resulting from a saturated aliphatic carbon chain of about 3 toabout 30 carbon atoms in length.

The chain or bridging group may be aliphatic, cyclic, or aromatic, or amixture thereof. It may contain saturated or unsaturated carbon atoms ora mixture of same with, for example, alkoxy groups (ethoxy, propoxy,isopropoxy, butoxy, and the like). It may also include or be madecompletely from alkoxy groups, glycerides, glycerols, and glycols. Thechain may contain hetero-atoms such as O, N, S, or Si and derivativessuch as siloxanes, non-protonated tertiary amines and the like. Thechain may be made from one or more cyclic or aromatic groups such as acyclohexane, a immidazole, a benzene, a diphenol, a toluene, or a xylenegroup or from more complex ring-containing groups such as a bisphenol ora benzidine. These are merely representative and are not meant to belimiting. Generally, however, the bridging group will not contain anionically charged species, other than the dianions or dications.

The diionic liquids of the present invention are generally salts,although they may exist as ions (+1, −1, +2, −2) in certaincircumstances. Thus, in most instances, each ion should have acounterion, one for each anion or cation. Charge should be preserved. Inthe case of a dianionic ionic liquid, two cations (including thoseidentified as C′ or C″) (or one dication) (including those identified asC) are required and in the case of a dicationic ionic liquid, two anions(including those identified as C′ or C″) (or one dianion) (includingthose identified as C) are required. The choice of anion can have aneffect of the properties of the resulting compound and its utility as asolvent. And, while anions and cations will be described in the contextof a single species used, it is possible to use a mixture of cations toform salts with a dianionic species to form a dianionic ionic liquid.The reverse is true for dications. For clarity sake, the salt-formingions will be referred to as counterions herein.

Cationic counterions can include any of the dicationic compoundspreviously identified for use in the production of dicationic ionicliquids. In addition, monoionic counterparts of these may be used. Thus,for example, quaternary ammonium, protonated tertiary amines,phosphonium, and arsonium groups are useful as cationic counterions fordianionic molecules to form dianionic ionic liquids in accordance withthe present invention.

Similarly, anionic counterions can be selected from any of the dianionicmolecules discussed herein useful in the creation of dianionic ionicliquids. These would include dicarboxylates, disulphonates, anddisulphates. The corresponding monoionic compounds may also be usedincluding carboxylates, sulphonates, sulphates and phosphonates.Halogens may be used as can triflate, NTf₂ ⁻, PF₆ ⁻, BF₄ ⁻ and the like.The counterions should be selected such that the diionic liquids havegood thermal and/or chemical stability and have a solid/liquidtransformation temperature and/or a liquid range as described herein.Finally, the ionic groups of the present invention can be substituted orunsubstituted. They may be substituted with halogens, with alkoxygroups, with aliphatic, aromatic, or cyclic groups, withnitrogen-containing species, silicon-containing species, withoxygen-containing species, and with sulphur-containing species. Thedegree of substitution and the selection of substituents can influencethe properties of the resulting material as previously described indiscussing the nature of the bridge or chain. Thus, care should be takento ensure that excessive steric hindrance and excessive molecular weightare avoided, that resulting materials does not lose its overallflexibility and that nothing will interfere with the ionic nature of thetwo ionic species.

The diionic liquids of the present invention can be used in pure or insubstantially pure form as carriers or as solvents. “Substantially” inthis context means no more than about 10% of undesirable impurities.Such impurities can be either other undesired diionic salts, reactionby-products, contaminants or the like as the context suggests. In anintended mixture of two or more DILS, neither would be considered animpurity. Because they are non-volatile and stable, they can berecovered and recycled and pose few of the disadvantages of volatileorganic solvents. Because of their stability over a wide liquid range,in some instances over 400° C., they can be used in chemical synthesisthat require both heating and cooling. Indeed, these solvents mayaccommodate all of the multiple reaction steps of certain chemicalsyntheses. Of course, these diionic liquids may be used in solventsystems with cosolvents and gradient solvents and these solvents caninclude, without limitation, chiral ionic liquids, chiral non-ionicliquids, volatile organic solvents, non-volatile organic solvents,inorganic solvents, water, oils, etc. It is also possible to preparesolutions, suspensions, emulsions, colloids, gels and dispersions usingthe diionic liquids.

In addition to discrete diionic salts and diionic liquid salts, it isalso possible to produce polymers of these materials. Polymers mayinclude the diionic salts within the backbone or as pendant groups andthey may be cross-linked or non-cross-linked.

In addition to being useful as solvents and reaction solvents, thedianionic liquids of the present invention can be used to performseparations as, for example, the stationary phase for gas-liquidchromatography. Dicationic ionic liquid salts, which may be used forexemplification include: (1) two vinyl imidazolium or pyrrolidiniumdications separated by an alkyl linkage chain (of various length) or (2)one vinyl imidazolium or pyrrolidinium cation separated an alkyl linkagechain (of various length) and connected to a methyl, ethyl, propyl, orbuylimidazolium cation or a methyl, ethyl, propyl, or butylpyrrolidiniumcation. See below. Any anionic counterion discussed may be used. Notethat the presence of unsaturated groups facilitates cross-linking and/orimmobilization.

Dianionic anions can also be used with either monocations or dicationsto form a variety of different ionic liquid combinations. When adication is used, anyone is used as charge balance must be preserved.The dianionic anions can be of the dicarboxylic acid type (i.e.,succinic acid, nonanedioic acid, dodecanedioic acid, etc), as shownbelow.

Diionic liquid salts can be coated on a capillary (or solid support) andoptionally, subsequently polymerized and/or cross-linked by, forexample, two general methods. In the first method, the ionic liquid arecoated via the static coating method at 40° C. using coating solutionconcentrations ranging from 0.15-0.45% (w/w) using solutions ofmethylene chloride, acetone, ethyl acetate, pentane, chloroform,methanol, or mixtures thereof. After coating of the ionic liquid iscomplete, the column is purged with helium and baked up to 100° C. Theefficiency of naphthalene is then evaluated to examine the coatingefficiency of the monomer ionic liquid stationary phase. If efficiencyis deemed sufficient, the column is then flushed with vapors ofazo-tert-butane, a free radical initiator, at room temperature. Afterflushing with the vapors, the column is then fused at both ends andheated in an oven using a temperature gradient up to 200° C. for 5hours. The column gradually cooled and then re-opened at both ends, andpurged with helium gas. After purging with helium gas overnight, thecolumn is then heated and conditioned up to 200° C. After conditioning,the column efficiency is then examined using naphthalene at 100° C. andthe stationary phase coated layer examined under a microscope. Note thatthe cross-linking process can, and often does, also cause immobilization“Immobilized” in the context of the invention means covalently orionically bound to a support or to another ionic liquid (includingdiionic liquid salts) or both. This is to be compared with ionic liquidswhich may be absorbed or adsorbed on a solid support. Solid support inthese particular instances were intended to include columns.

It is not necessary, however, to cross-link these materials prior totheir use in GC. They may be adsorbed or absorbed in a column, or indeedon any solid support. However, at higher temperatures, their viscositymay decrease and they can, in some instances, flow and collect asdroplets which can change the characteristics of the column.

Another method involves adding up to 2% of the monomer weight of2,2′-azobisisobutyronitrile (“AIBN”) free radical initiator to thecoating solution of the monomer. The capillary column is then filledwith this solution and coated via the static coating method. Aftercoating, the capillary column is then sealed at both ends and placed inan oven and conditioned up to 200° C. for 5 hours. The column isgradually cooled and then re-opened at both ends, and purged with heliumgas. After purging with helium gas overnight, the column is then heatedand conditioned up to 200° C. After conditioning, the column efficiencyis then examined using naphthalene at 100° C. and the stationary phasecoated layer examined under a microscope.

In addition to the free radical polymerization of an alkene, otherpolymerization reactions involving other functional groups eitherattached to the aromatic ring of the cation, the linkage chainconnecting two cations (to form a dication), or the anion can beachieved. Examples of such reactions may include cationic and anionicchain growth polymerization reactions, Ziegler-Natta catalyticpolymerization, and step-reaction polymerization. The use of twodifferent monomers to form copolymers through addition and blockcopolymerization can also be achieved. Additionally, condensationpolymerization can be used to connect through functional groups such asamines and alcohols. All polymerization and cross-linking reactionsdiscussed in the following 2 references can be used: “ComprehensivePolymer Science—The synthesis, Characterization, Reactions andApplications of Polymers” by Sir Geoffrey Allen, FRS; “ComprehensiveOrganic Transformations: a guide to functional group preparations” byRichard C. Larock. 2nd Edition. Wiley-VCH, New York. Copyright, 1999.ISBN: 0471190314.

The production of these 39 dicationic liquid: are described. Thefollowing materials were used: 1-methylimidazole; 1-methylpyrrolidine;1-butylpyrrolidine; 1,2-dimethylimidazole; 1-butylimidazole;1-benzylimidazole; 1,3-dibromopropane; 1,6-dibromohexane;1,9-dibromononane; 1,12-dibromododecane; 1-bromo-3-chloropropane;hexafluorophosphoric acid, sodium tetrafluoroborate,N-lithiotrifluoromethylsulfonimide, silver nitrate, and phosphoruspentoxide were all purchased from Aldrich (Milwaukee, Wis.).Hexafluorophosphoric acid is toxic and corrosive and must be handledwith care. Acetone, ethyl acetate, and 2-propanol were purchased fromFisher Scientific (Fair Lawn, N.J.). Untreated fused silica capillarytubing (0.25-mm i.d.) was purchased from Supelco (Bellefonte, Pa.).

The following diionic salts may be produced. (See Tables 1, 2 and 3.)

TABLE 1 Physicochemical properties of imidazolium-based dicationic ionicliquids^(a) Temperature of^(b) Molecular Surface Solid/Liquid WeightTension Density Transformation Refractive Miscibility Miscibility #Ionic Liquid (g/mol) (dynes/cm) (g/cm³) (° C.) Index with Heptane withWater 1 C₃(mim)₂-Br 366.10 — —  162^(c) — Immiscible Miscible 2C₃(mim)₂-NTf₂ 766.58 44.7 1.61  −4 1.440 Immiscible Immiscible 3C₃(mim)₂-BF₄ 379.90 — — 117 — Immiscible Miscible 4 C₃(mim)₂-PF₆ 496.22— — 131 — Immiscible Immiscible 5 C₆(mim)₂-Br 408.18 — — 155 —Immiscible Miscible 6 C₆(mim)₂-NTf₂ 808.66 44.2 1.52 >−14, <−4 1.441Immiscible Immiscible 7 C₆(mim)₂-BF₄ 421.98 — —  92 — ImmiscibleMiscible 8 C₆(mim)₂-PF₆ 538.30 — — 136 — Immiscible Immiscible 9C₉(mim)₂-Br 450.26 59.6 1.41  6 1.549 Immiscible Miscible 10C₉(mim)₂-NTf₂ 850.74 43.1 1.47 −14 1.442 Immiscible Immiscible 11C₉(mim)₂-BF₄ 464.06 61.2 1.33  −4 1.469 Immiscible Miscible 1C₃(mim)₂-Br 366.10 — —  162^(c) — Immiscible Miscible 2 C₃(mim)₂-NTf₂766.58 44.7 1.61  −4 1.440 Immiscible Immiscible 3 C₃(mim)₂-BF₄ 379.90 —— 117 — Immiscible Miscible 4 C₃(mim)₂-PF₆ 496.22 — — 131 — ImmiscibleImmiscible 5 C₆(mim)₂-Br 408.18 — — 155 — Immiscible Miscible 6C₆(mim)₂-NTf₂ 808.66 44.2 1.52 >−14, <−4 1.441 Immiscible Immiscible 7C₆(mim)₂-BF₄ 421.98 — —  92 — Immiscible Miscible 8 C₆(mim)₂-PF₆ 538.30— — 136 — Immiscible Immiscible 9 C₉(mim)₂-Br 450.26 59.6 1.41  6 1.549Immiscible Miscible 10 C₉(mim)₂-NTf₂ 850.74 43.1 1.47 −14 1.442Immiscible Immiscible 11 C₉(mim)₂-BF₄ 464.06 61.2 1.33  −4 1.469Immiscible Miscible 12 C₉(mim)₂-PF₆ 580.38 — —  88 — ImmiscibleImmiscible 13 C₁₂(mim)₂-Br 492.34 57.9 1.27 −17 1.540 ImmiscibleMiscible 14 C₁₂(mim)₂-NTf₂ 892.82 42.3 1.40 −26 1.443 ImmiscibleImmiscible 15 C₁₂(mim)₂-BF₄ 506.14 55.8 1.26 −19 1.503 ImmisciblePartially Miscible 16 C₁₂(mim)₂-PF₆ 622.46 53.4 1.36  9 1.436 ImmiscibleImmiscible 17 C₉(bim)₂-Br 534.42 53.1 1.27  >0, <23 1.545 ImmiscibleMiscible 18 C₉(bim)₂-NTf₂ 934.90 38.0 1.35 >−42, <−8 1.446 ImmiscibleImmiscible 19 C₉(bim)₂-BF₄ 548.22 50.4 1.20 >−42, <−8 1.503 ImmisciblePartially Miscible 20 C₉(bim)₂-PF₆ 664.54 48.0 1.30  >0, <23 1.439Immiscible Immiscible 21 C₃(m₂im)₂-Br 394.15 — — 298 — ImmiscibleMiscible 22 C₃(m₂im)₂-NTf₂ 794.63 — —  91 — Immiscible Immiscible 23C₃(m₂im)₂-PF₆ 524.27 — — 264 — Immiscible Immiscible 24 C₉(m₂im)₂-Br478.31 — — 174 — Immiscible Miscible 25 C₉(m₂im)₂-NTf₂ 878.79 43.51.47 >−42, <−8 1.448 Immiscible Immiscible 26 C₉(m₂im)₂-BF₄ 492.11 58.11.31  >0, <23 1.456 Immiscible Miscible 27 C₉(m₂im)₂-PF₆ 608.43 — — 130— Immiscible Immiscible 28 C₁₂(benzim)₂-Br 644.53 — — 151 — ImmiscibleImmiscible 29 C₁₂(benzim)₂-NTf₂ 1045.01 41.5 1.37 >−8, <0 1.482Immiscible Immiscible 30 C₁₂(benzim)₂-PF₆ 774.65 47.4 1.27 −15 1.484Immiscible Immiscible ^(a)Patents pending ^(b)Difficulty arises indetermining the melting points of some ionic liquids as they prefer theglass-state. Therefore, for some ionic liquids in which the exactmelting point/glass transition temperature could not be easilydetermined, a temperature range is provided. A detailed discussionrelated to the polymorphic nature of many of these ionic liquids isprovided in the section titled “Crystal Structures of Geminal DicationicIonic Liquids” ^(c)This ionic liquid exhibited physico-chemicalproperties very similar to the 1-butyl-3-methylimidazolium chlorideionic liquid making it difficult to fully characterize.

TABLE 2 Physicochemical properties of pyrrolidinium-based dicationicionic liquids^(a) Temperature of^(b) Molecular Surface Solid/LiquidWeight Tension Density Transformation Refractive Miscibility Miscibility# Ionic Liquid (g/mol) (dynes/cm) (g/cm³) (° C.) Index with Heptane withWater 31 C₃(mpy)₂-Br 372.18 — —    51^(c) — Immiscible Miscible 32C₃(mpy)₂-NTf₂ 772.67 — — 206 — Immiscible Immiscible 33 C₃(mpy)₂-PF₆502.30 — — 359 — Immiscible Immiscible 34 C₉(mpy)₂-Br 456.34 — — 257 —Immiscible Miscible 35 C₉(mpy)₂-NTf₂ 856.83 42.2 1.41 >−8, <0 1.436Immiscible Immiscible 36 C₉(mpy)₂-PF₆ 586.46 — — 223 — ImmiscibleImmiscible 37 C₉(bpy)₂-Br 540.50 — — 216 — Immiscible Miscible 38C₉(bpy)₂-NTf₂ 940.98 — —  84 — Immiscible Immiscible 39 C₉(bpy)₂-PF₆670.62 — — 249 — Immiscible Immiscible ^(a)Patents pending^(b)Difficulty arises in determining the melting points of some ionicliquids as they prefer the glass-state. Therefore, for some ionicliquids in which the exact melting point/glass transition temperaturecould not be easily determined, a temperature range is provided. Adetailed discussion related to the polymorphic nature of many of theseionic liquids is provided in the section titled “Crystal Structures ofGeminal Dicationic Ionic Liquids” ^(c)This ionic liquid exhibitedphysico-chemical properties very similar to the1-butyl-3-methylimidazolium chloride ionic liquid making it difficult tofully characterize.

TABLE 3 Imidazolium-based Dicationic Ionic Liquids

Pyrrolidinium-based Dicationic Ionic Liquids

Also produced in accordance with the invention are:

Examples of chiral ionic liquids include the following: Chiraldicationic IL

Chiral dianionic IL

Polymerizable chiral IL

Polymerizable dicationic dicationic IL

Note that some of the salts reflected in EXAMPLE A—Tables 1 and 2 maynot reflect the correct number of anions; usually 2 (see EXAMPLE A—Table3). Note that the names of the compounds found in EXAMPLE A—Tables 1 and2, are found in EXAMPLE A—Table F. Compounds 1, 5, 9, and 13 weresynthesized by reacting one molar equivalent of 1,3-dibromopropane;1,6-dibromohexane; 1,9-dibromononane; and 1,12-dibromododecane,respectively, with two molar equivalents of 1-methylimidazole at roomtemperature. Compound 17 was synthesized by reacting one molarequivalent of 1,9-dibromononane with two molar equivalents of1-butylimidazole at room temperature. Compounds 21 and 24 weresynthesized by refluxing one molar equivalent of 1,3-dibromopropane and1,9-dibromononane, respectively, with 1,2-dimethylimidazole dissolved in125 mL 2-propanol for 24 hours. Compound 28 was synthesized by refluxingone molar equivalent of 1,12-dibromododecane with two molar equivalentsof 1-benzylimidazole in 100 mL of 2-propanol for 24 hours. Followingcomplete reaction (as monitored by NMR), the products were all purifiedby extraction with ethyl acetate and dried under a P.sub.2O.sub.5vacuum.

Compounds 31 and 34 were produced by refluxing one molar equivalentamount of 1,3-dibromopropane and 1,9-dibromononane with two equivalentsof 1-methylpyrrolidine in 100 mL of 2-propanol for 24 hours. Compound 37was synthesized by refluxing two molar equivalents of 1-butylpyrrolidinewith one equivalent of 1,9-dibromononane in 100 mL of 2-propanol for 24hours. These salts were also extracted with ethyl acetate and driedunder vacuum. All metathesis reactions involvingN-lithiotrifluoromethylsulfonimide, hexafluorophosphoric acid, andsodium tetrafluoroborate were performed using previously publishedprocedures. Ionic liquids formed via metathesis reactions were testedwith silver nitrate to ensure no halide impurities remained.

All thirty-nine ionic liquid samples were characterized using ¹H NMR andelectrospray ionization (ESI) mass spectrometry. ¹H NMR spectra (400MHz) were recorded in deuterated DMSO.

Surface tension values were measured at room temperature (23° C.) usinga Model 20 DuNuoy Tensiometer (Fisher Scientific, Fair Lawn, N.J.)equipped with a platinum-iridium ring with a mean circumference of 5.940cm and a ring/wire radius of 53.21. The densities of the ionic liquidsor, more correctly, the temperature of solid/liquid transformation (usedsynonymously except as indicated otherwise explicitly or by context)were determined at 23° C. by placing 2.0 mL of the ionic liquid in a 2.0mL volumetric tube and weighing by difference. The melting points of theionic liquids were determined using a Perkin Elmer Pyris 1 DifferentialScanning calorimeter (Boston, Mass.). Typical methods involved using a10° C./min temperature ramp to determine and identify the first andsecond order thermal transitions. Melting points could not be easilydetermined for all compounds. For solid compounds, the melting pointswere verified using a capillary melting point apparatus. Refractiveindex measurements were conducted at 23° C. using a Bausch & LombAbbe-3L refractometer.

The preparation of the capillary columns for inverse gas-liquidchromatographic analysis was performed using a previously describedprocedure. All capillary columns had efficiencies between 2100 to 2500plates/meter. Characterization of the capillary columns and probemolecule descriptions are listed in supplemental information. Multiplelinear regression analysis (MLRA) and statistical calculations wereperformed using the program Analyse-it (Microsoft, USA).

EXAMPLE A Tables 1, 2, and 3 give the structures of the two classes (39compounds) of geminal dicationic ionic liquids synthesized andcharacterized. Ionic liquids containing imidazolium-based dications withdifferent alkyl linkage chain lengths connecting the cations and/ordifferent alkyl substituents on the imidazolium moiety comprise onegroup of ionic liquids. In most cases, each geminal dicationic entitywas paired with four different anions (Br⁻, NTf₂ ⁻, BF₄ ⁻, and PF₆ ⁻,EXAMPLE A—Table 3). Pyrrolidinium-based geminal dications with differentalkyl linkage chain lengths connecting the cationic and/or differentalkyl substituents on the pyrroldinium group are also shown in EXAMPLEA—Table 3. For each dication in this class, separate ionic liquidscontaining three anions (Br⁻, NTf2, and PF6) were synthesized. EXAMPLE ATables 1 and 2 give the physicochemical properties for these thirty-ninegeminal ionic liquids. Surface tension, density, melting point, andrefractive index values were recorded for those samples that wereliquids at room temperature. For samples that were solids at roomtemperature, only the melting point was determined. Themiscibility/solubility of all ionic liquids in both heptane and waterare indicated as well.

Surface Tension. Plots of surface tension data are shown in FIG. 1 forseveral geminal room temperature ionic liquids. The length of the alkyllinkage chain separating the dications is observed to have only smalleffects on the surface tension. Considering ILs 2, 6, 10, and 14(EXAMPLE A Tables 1, 2, and/or 3) which all contain thebis(trifluoromethylsulfonyl)imide (NTf₂ ⁻) anion and 3-methylimidazoliumcations separated by 3, 6, 9 and 12 carbon linkage chains, respectively,it is apparent that increasing the length of the connecting linkagechain slightly decreases the surface tension (.about.2.4 dynes/cm). Asimilar trend is observed for the ionic liquids containing other anions(e.g., BF₄ ⁻, Br⁻, PF₆ ⁻). These results are quite different from thoseobtained for monocationic ionic liquids by Law, et al. It was reportedthat the surface tension for a series of1-alkyl-3-methylimidazolium-based ionic liquids containing 4, 8, and 12carbon alkyl groups in the one position of the imidazole ring (refer toEXAMPLE A Table 3 for the ring numbering of the imidazolium cation)significantly decreased with increasing alkyl chain length. The largestdecrease in surface tension was observed between1-butyl-3-methylimidazolium hexafluorophosphate and1-dodecyl-3-methylimidazolium hexafluorophosphate in which the totaldecrease in surface tension was nearly 20 dynes/cm at 330 K. It was alsoproposed that for a fixed cation at a specific temperature, the compoundwith the larger anion would possess a higher surface tension. However,our data indicates that this is not true for the geminal dicationicionic liquids, and if anything, is opposite to what was observedpreviously for the monocationic-type ionic liquids (EXAMPLE A Tables 1and 2).

Diionic liquids 17-20 contain nonpolar butyl groups in the threeposition of the imidazolium rings. The surface tension values aresignificantly smaller (11%-17%) than those of diionic liquids 9-12 and13-16 which contain the 3-methylimidazolium dications separated by anonane and dodecane linkage chain, respectively. This data seems toindicate that the alkyl substituent located on the three position of theimidazolium ring plays a more important role in lowering the surfacetension than the alkyl linkage chain that separates the geminaldications.

Replacing hydrogen with a methyl group on the two position of theimidazolium ring (refer to EXAMPLE A—Tables 1, 2, and 3) has littleeffect on the surface tension. In the case of diionic liquids 25 and 26containing the 2,3-dimethylimidazolium geminal dications separated by anonane linkage chain with NTf₂ ⁻ and BF₂ ⁻ anions, respectively, thesurface tension values are similar to the corresponding3-methylimidazolium dications (diionic liquids 10 and 11) alsocontaining the nonane connecting chain. Overall, this data indicatesthat as the alkyl chain in the 3-position of the imidazolium ringincreases in length, the surface tension decreases much more drasticallythan corresponding increases in the length of the connecting linkagechain.

Density. As shown in FIG. 2, the densities of the 3-methylimidazoliumgeminal dicationic ionic liquids were found to be anion dependent and todecrease with increasing length of the hydrocarbon linkage chain. Whileincreases in the linkage chain decreases the density of these ionicliquids, the nature of the anion has a greater influence, with densitiesin the order of NTf₂ ³¹ >PF₆ ⁻>Br>BF₄ (EXAMPLE A Tables 1, 2, and FIG.2). The decrease in density with increasing alkyl chain length has beenreported previously for a large series of 1-alkyl-3-methylimidazoliumionic liquids.

When the methyl group on the three position of the imidazolium ring isreplaced with a butyl group, the density decreases for all ionic liquidsin the series, regardless of the anion (compare 9-12 to 17-20, Table 1).However, by replacing the hydrogen at the two position of the ring witha methyl group, the density does not appear to change (see 10-11 and25-26, EXAMPLE A—Table 1).

Melting Points. From this study, four main factors were found to affectthe melting points of these geminal-dicationic ionic liquids. Thesefactors which apply to dianions as well are: (1) the length and type ofthe linkage chain or bridge separating the geminal diions, (2) thenature of the diions (e.g., imidazolium versus pyrrolidinium), (3) thesubstituents and their placement on the dianions, and (4) the nature ofthe counterion.

Considering first the 3-methylimidazolium-based dicationic ionicliquids, longer bridging groups generally result in a lowering of themelting points. This observation applies to diionic liquids generally.In all of the above-noted cases except for the geminal dications withNTf₂ ⁻ anions, which were all liquids regardless of the linkage chainused, compounds containing three and six carbon linkage chains weresalts with relatively high melting points. By connecting the3-methylimidazolium dications with a nonane linkage chain, all sampleswere room temperature ionic liquids except for the hexafluorophosphatesalt, which had a melting point of 88° C. When the dications wereconnected by a dodecane linkage chain, however, all compounds were roomtemperature ionic liquids. Looking more generally at the dianions anddications that can be used to make diionic liquids in accordance withthe present invention, the chain length between the ionic species shouldbe longer than the length of a 2 carbon chain, and no longer than a 40carbon chain. Preferably, chain lengths are equivalent to the length ofa 3 to 30 carbon chain. The degree and types of substituents, if any,may have an effect on length as well, the larger the molecule,generally, the higher its temperature of solid/liquid transformation.Therefore, any chain length, any chain content and any chainsubstitution pattern may be used, as long as the melting point of theresulting diionic liquid salt is less than about 400° C., preferablyabout 100° C. or less, preferably about 60° C., more preferably aboutroom temperature or less (25° C.).

In addition to the effect of the different length and types of bridgesconnecting the dications, the anion also played a role in determiningthe melting point. In nearly very case of the imidazolium dications, themelting points increased in the following order: NTf₂ ⁻<BF₄ ⁻<PF₆ ⁻<Br⁻(EXAMPLE A—Tables 1 and 2).

Other anions which can be used to form dicationic ionic liquids include,without limitation, trifilates, carboxylates, sulfonates and sulfates(both mono- and poly-anionic species). Dianionic ionic liquids can beproduced from any dianion which can form a stable salt, preferably whichhas a melting point below 400° C., more preferably at or below 100° C.,most preferably at or below room temperature (25° C.). These includedicarboxylate, disulfonate and disulfates. Mixed dianions, one madefrom, for example, a dicarboxylate and a disulfate, are also desirable.Cations or counterions for these include, again without limitation, thedications listed in EXAMPLE A—Tables 1 and 2, as well as theirmonocationic counterparts. This is as long as they can form a stablediionic salt and have a melting point as described above.

The substituents and their position on the imidazolium ring alsoaffected the melting points of these compounds. These sameconsiderations apply to substituted anions as well. Considering 17-20which contain the 3-butylimidazolium dications connected by a nonanelinkage chain, the melting points were lowered significantly byreplacing the methyl group (see 9-12) with a butyl group. In the case of12, which consists of the 3-methylimidazolium dications connected by anonane linkage chain with the PF₆ ⁻ anion, the melting point isdecreased by nearly 60° C. by replacing the methyl groups with butylgroups to form 20. In addition, methylation of the 2-positions of theimidazolium dications significantly increases the melting point of thesecompounds (see 21-27, EXAMPLE A—Table 1). In the case of 21 whichcontains the 2,3-dimethyimidazolium dication connected by a propanelinkage chain, the melting point is nearly 135° C. higher than thecorresponding 3-methylimidazolium dication also connected by a propanelinkage chain. Others have previously reported the melting points for1-ethyl-3-methylimidazolium bromide to be 79° C. whereas the meltingpoint for 1-ethyl-2,3-dimethylimidazolium bromide was found to be 141°C., a difference of nearly 62° C. While the methyl group on the twoposition of the imidazolium ring has little effect on the surfacetension and density of the geminal dicationic ionic liquids, it is seento have a profound effect on their melting points, more so for thedicationic ionic liquids than for the traditional1-alkyl-3-methylimidazolium ionic liquids.

Finally, by replacing the 3-methylimidazolium dication with the3-benzylimidazolium dication (28-30) and connecting them by a dodecanebridge, the melting points appear higher compared to the3-methylimidazolium series, especially in the case of the bromide salt.

In general, the melting points of the pyrroldinium-based geminaldicationic compounds are significantly higher than their correspondingimidazolium analogues. Indeed, only two of their NTf₂ ⁻ salts can beconsidered ionic liquids. However, as will be discussed (vide infra),these particular RTILs may have the greatest thermal stability and otherhighly useful and interesting properties.

The melting points for the pyrrolidinium-based dications show similartrends to the imidazolium-based salts. In the two cases involving thepropane and nonane linkage chains, the melting point decreases as thelinkage chain becomes longer. However, in contrast to theimidazolium-based dications, the pyrrolidinium-based dications are stillrelatively high melting solids when separated by a nonane alkyl chain.Additionally, substituting a butyl group instead of a methyl group onthe quaternary amine of the pyrrolidinium cation causes a decrease inthe melting point for the bromide dication but an increase in themelting point for the dications containingbis(trifluoromethylsulfonyl)imide and hexafluorophosphate anions.

From the data in EXAMPLE A—Tables 1 and 2, it appears that longer alkyllinkage chains and long aliphatic substituents on the quaternary amineproduce either low melting salts or room temperature ionic liquids.Further, the NTf₂ ⁻ salts have lower melting points than correspondingsalts with other anions. The contributions of the linkage chain(bridge), and other substituents on the geminal dicationic salts, to thenumber of possible conformational states (and possibly crystalpolymorphs) will be considered in the crystal structure section of thispaper.

Solubility. The solubility behavior of all thirty-nine geminaldicationic ionic liquids in water and heptane also was explored. None ofthe dicationic ionic liquids were soluble in heptane. However, most ofthe ionic liquids containing bromide and tetrafluoroborate anions weresoluble in water. Nevertheless, for the tetrafluoroborate ionic liquids,it was found that by using a long linkage chain and a more hydrophobicalkyl substituent on the three position of the imidazole ring (seecompounds 15 and 19), the solubility of the salt in water decreases. Ingeneral, the solubility behavior of the geminal dicationic ionic liquidsin both water and heptane was quite similar to the monocationic ionicliquids with NTf₂ ⁻ and PF₆ ⁻ salts being immiscible with water and Br⁻and BF₄ ⁻ salts being miscible with water. Indeed, the monoioniccounterparts of the diionic liquid salts of the present invention are agood predicator of the solubility of a diionic liquid salt.

In the case of the dicationic ionic liquid 28 which consists of the3-benzylimidazolium dication separated by a dodecane linkage chain andbromide anion, the hydrophobicity of the dication evidently overridesthe coordinating nature of the bromide anion to make this particularionic liquid insoluble in water. This is a good example that theproperties of the individual cations and anions can be balanced andchanged in order to produce ionic liquids (or solids) with the desiredproperties and characteristics.

Thermal Stability. The thermal stabilities of the geminal dicationicionic liquids were found to be significantly higher than what has beenobserved for many traditional imidazolium-based ionic liquids. Thermalstabilities were measured by immobilizing an approximate 0.15-0.20microns film of the ionic liquid on the inner wall of a fused silicacapillary. The capillary was then heated slowly in an oven and a verysensitive flame ionization detector (or mass spectrometer) used todetect any volatilization or decomposition of the ionic liquid. Thereare several advantages of using this set-up to measure the thermalstabilities of ionic liquids. The thermal stability is measured in theabsence of oxygen by purging the capillary with a continuous flow of aninert gas such as helium, hydrogen, or nitrogen. In addition, thedetection limit of the detector is very low (about 10 ppm to 10 ppb,depending on the compound) allowing for very sensitive detection of anythermally induced decomposition/volatilization products from the ionicliquid. Finally, this approach can use mass spectrometry detection todetermine the likely volatilization/decomposition products.

FIG. 3 shows a thermal stability diagram containing three traditionalionic liquids and four dicationic ionic liquids. The traditional ionicliquids have thermal stabilities ranging from 145° C.(1-butyl-3-methylimidazolium chloride) to 185° C.(1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide).However, the thermal stabilities of the geminal dicationic ionic liquidsare observed to range from 330° C. to 400° C., depending on the cationused. The highest thermal stability (>400° C.) was obtained with theC₉(mpy₂-NTf₂ (35) ionic liquid (1-methylpyrrolidinium dication separatedby a nonane linkage chain) while the lowest volatilization/decompositiontemperature (330° C.) was observed for the C₉(bpy)₂-NTf₂ (38,1-butylpyrrolidinium dication separated by a nonane linkage chain) ionicliquid. The maximum thermal stabilities of C₉(mim)₂-NTf₂(10,1-methylimidazolium dication) and C₁₂(benzim)₂-NTf₂(29,3-benzylimidazolium dication separated by a dodecane linkage chain)were observed to be nearly identical (350-360° C.). In most cases,slight to moderate decomposition/volatilization of the dicationic ionicliquids were observed at these high temperatures. However, due tocharring of the polyimide coating on the outside of the fused silicacapillary tubing at these high temperatures, the ionic liquids were onlytested up to 400° C.

While the physical and thermal properties of the dicationic ionicliquids are quite impressive, another interesting fact is that some ofthese compounds possess useful liquid ranges in excess of 400° C. andone of these (C₉(mpy)₂-NTf₂) 35 has a stable liquid range of .about. −4°C. to >400° C. This property will undoubtedly ensure their use for awide variety of applications in which this large liquid range and highthermal stability can be exploited. In accordance with one aspect of thepresent invention, the ionic liquids of the present invention, which aresalts of a dianion or dication, are stable. Stability in the context ofthe present invention means that they will neither substantiallydecompose nor volatilize at a temperature of under about 200° C. whenmeasured by inverse gas chromatography as described herein. Morepreferably, the stable ionic liquids of the present invention which aredianionic or dicationic salts, are stable in that they will notsubstantially decompose or volatilize at a temperature of under about300° C.

In FIG. 3, it is believed that the detector response shown for compoundsD, E and F, between approximately 200 and approximately 300° C. are fromimpurities and not from the compounds tested. Still, less than 10% ofthe weight of the material tested decomposes or volatilizes when exposedto 200° C. or in preferred embodiments, 300° C., for an hour, they canbe said to be stable in accordance with the present invention.

In particularly preferred embodiments in accordance with the presentinvention, dianionic or dicationic ionic liquid salts are provided,which are stable in that they will neither substantially decompose norsubstantially volatilize at a temperature of under 200° C. and will havea temperature of solid/liquid transformation of 400° C. or less. Morepreferably will have a temperature of solid/liquid transformation of100° C. or less, most preferably will have a temperature of solid/liquidtransformation of 25° C. or less.

As mentioned previously, the diionic liquids (salts of dianions anddications as described herein) have an important use because of theirstability at wide ranges of temperature and unique liquid properties.Many of these liquids have unexpectedly low temperatures of solid-liquidtransformation, which from a fundamental standpoint depends upon theenergy of their crystal lattice. There are well-known and rather crucialbarriers to precisely calculating these energies, i.e., the truedetermination of atom-atom potentials. On the other hand, the accuratemeasurement (required for comparison) of solid-liquid transformationtemperatures for this family of ionic compounds also have difficulties.The transformation is not sharp in time and the peaks on DSC curvesbecome very broad. Formally speaking, the temperature of thistransformation can be very different from the true melting point whichis the temperature of thermodynamic equilibrium between solid and liquidstates.

Solvation Characteristics. We have previously reported that the Abrahamsolvation model, a linear free energy approach that utilizes inversegas-liquid chromatography to describe the solvation properties of aliquid, can be used to characterize room temperature ionic liquids.Described by equation 1, the model provides the so-called “interactionparameters” (r, s, a, b, l) by using multiple linear regression analysisto fit the retention factor (k, determined chromatographically) to thesolute descriptors (R₂, π₂ ^(H)α_(2H), β₂ ^(H), log L¹⁶) for a widevariety of probe solute molecules.log k=c+rR ₂ +sπ ₂ ^(H) +bβ ₂ H+1 log L ¹⁶  [1]

The solvation properties of four dicationic ionic liquids (see EXAMPLE ATable 4) were evaluated and the interaction parameters compared to thoseobtained for their traditional monocationic analogues1-butyl-3-methylimidazolium and 1-butyl-1-methylpyrrolidinium ionicliquids.

TABLE 4 Comparison of interaction parameters between monocationic anddicationic ionic liquids. Interaction Parameters^(a) Temp (° C.) c r s ab l n R² F C₄(mim)₂-NTf₂ 40 −2.94 0.25 2.01 2.11 0.50 0.56 33 0.99356.70 (0.13) (0.09) (0.12) (0.11) (0.13) (0.03) (0.11) 70 −2.91 0.221.78 1.77 0.45 0.44 32 0.99 370.42 (0.11) (0.10) (0.11) (0.09) (0.14)(0.03) (0.09) 100 −3.06 0.20 1.69 1.57 0.33 0.37 31 0.98 253.79 (0.13)(0.09) (0.10) (0.08) (0.13) (0.03) (0.09) C₉(mim)₂-NTf₂ (10) 40 −2.860.16 1.81 1.83 0.47 0.62 32 0.98 257.15 (0.14) (0.11) (0.14) (0.10)(0.17) (0.04) (0.12) 70 −2.95 0.11 1.76 1.75 0.20 0.51 33 0.99 644.20(0.09) (0.07) (0.08) (0.07) (0.10) (0.02) (0.07) 100 −3.06 0.11 1.641.50 0.15 0.43 32 0.99 545.32 (0.08) (0.06) (0.07) (0.06) (0.09) (0.02)(0.07) BMIM-NTf₂ ^(a) (1-butyl-3-methylimidazoliumbis[(trifluoromethylsulfonyl)imide] 40 −2.87 0 1.89 2.02 0.36 0.63 330.99 459.64 (0.10) (0.08) (0.10) (0.10) (0.12) (0.03) (0.09) 70 −3.03 01.67 1.75 0.38 0.56 35 0.99 413.65 (0.09) (0.08) (0.09) (0.09) (0.11)(0.02) (0.09) 100 −3.13 0 1.60 1.55 0.24 0.49 32 0.98 240.13 (0.12)(0.09) (0.10) (0.10) (0.12) (0.03) (0.09) C₉(mpy)₂-NTf₂ (35) 40 −2.830.27 1.71 1.98 0.32 0.62 30 0.99 377.84 (0.12) (0.10) (0.12) (0.10)(0.15) (0.03) (0.10) 70 −2.85 0.34 1.52 1.65 0.35 0.48 32 0.99 419.32(0.11) (0.09) (0.11) (0.08) (0.13) (0.03) (0.09) 100 −2.99 0.23 1.491.48 0.15 0.42 30 0.99 339.79 (0.10) (0.09) (0.10) (0.08) (0.14) (0.03)(0.08) BMPY-NTf₂ ^(b) (1-butyl-1-methylpyrrolidiniumbis[(trifluoromethylsulfonyl)imide] 40 −2.78 0 1.69 2.08 0.16 0.68 340.98 321.99 (0.11) (0.09) (0.11) (0.12) (0.14) (0.03) (0.11) 70 −2.80 01.53 1.78 0 0.56 34 0.99 393.23 (0.10) (0.08) (0.09) (0.08) (0.11)(0.02) (0.09) 100 −2.92 0 1.44 1.55 0 0.48 32 0.99 358.08 (0.09) (0.07)(0.08) (0.07) (0.09) (0.02) (0.08) C₁₂(benzim)₂-NTf₂ (29) 40 −2.94 0.111.65 1.96 0.84 0.66 33 0.99 522.89 (0.11) (0.08) (0.11) (0.08) (0.13)(0.03) (0.08) 70 −3.07 0.07 1.62 1.75 0.57 0.56 30 0.99 888.94 (0.08)(0.05) (0.08) (0.06) (0.09) (0.02) (0.06) 100 −3.12 0 1.47 1.44 0.520.46 30 0.99 478.94 (0.09) (0.09) (0.06) (0.10) (0.02) (0.07) ^(a)r =interaction via nonbonding and □-electrons, s =dipolarity/polarizability, a = hydrogen bond basicity, b = hydrogen bondacidity, l = dispersion forces, n = number of probe molecules subjectedto multiple linear regression analysis, R² = statistical correlationcoefficient, F = Fisher coefficient. Values in parenthesis are thestandard deviations for each interaction parameter. ^(b)Values takenfrom reference 31

Nearly all interaction parameters of the dicationic ionic liquidsC₄(mim)₂-NTf₂ and C₉(mim)₂-NTf₂ (10) are similar to the correspondingmonomer-type ionic liquids, 1-butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. This is also observed for thepyrrolidinium dication, C₉(mpy)₂-NTf₂ (35), as it differs from themonomer-type analogue (1-butyl-1-methylpyrrolidiniumbis(trifluoromethylsulfonyl)imide). This indicates that the well-knownand highly useful solvation properties of traditional RTILs are verysimilar to those of the geminal dicationic RTILs. The only interactionparameter that is statistically different between the three ionicliquids is the “r” interaction parameter, namely the ability of theionic liquid to undergo .π-π and n-π interactions with probe solutemolecules. Because the pyrroldinium cation is not aromatic, the higher rvalues may be due to the anion as each anion contains two sulfone groupsthat are capable of undergoing such interactions. However, this was notobserved for the traditional ionic liquids evaluated previously in ourstudy.

Finally, the interaction parameters for the 3-benzylimidazolium geminaldication separated by a dodecane linkage chain with the NTf₂ ⁻ anion(29) appear similar to those observed previously for1-benzyl-3-alkyl-imidazolium ionic liquids. However, the hydrogen bondacidity term, b, is larger for the geminal dicationic ionic liquid. Thismay be due to the increased acidity of the proton at the 2-position ofthe imidazolium ring induced by the electron withdrawing benzyl group.

As noted earlier, the viscosity of some diionic salts decreases sharplywith increasing temperature. Consequently at high temperatures,previously uniform coated capillaries, particularly ones that areprepared by adsorption or absorption, rather than immobilization, canexperience film disruption (due to flow, etc.). When a uniformly coatedGC capillary, for example, slowly changes to a nonuniformly coatedentity, the analyte retention times and efficiency tend to decrease.

To overcome these issues, where necessary, and in accordance withanother aspect of the present invention, there is provided a processwhich includes the free radical reaction of ionic liquid monomers toprovide a more durable and robust stationary phase, as well as thecross-linked and/or immobilized stationary phases and the columns thatinclude same. By partially crosslinking the ionic liquid stationaryphase using a small percentage of free radical initiator, highefficiency capillary columns are produced that are able to endure hightemperatures with little column bleed. It was found that low to moderatetemperature separations (30° C.-280° C.) can be carried out with highselectivity and efficiency using special partially cross-linked ionicliquid stationary phase mixtures. These stationary phases retain their“gelatinous,” “semi liquid,” amorphous state. For separations conductedat higher temperatures (300° C.-400° C.), more highlycross-linked/immobilized stationary phases are well-suited to providehigh selectivity and efficient separations with low column bleed. Theeffect of different functionalized ionic liquid salt mixtures andinitiator concentrations is studied for these two types of stationaryphases. The accomplished goal is to maximize their separationefficiency, thermal stability, and column lifetime, without sacrificingthe unique selectivity of the stationary phase.

The following materials were used to illustrate the unique advantages ofcross-linked stationary phases comprising diionic liquid salts inaccordance with the present invention: 1-vinylimidazole, 1-bromohexane,1-bromononane, 1-bromododecane, 1,9-dibromononane, 1,12-dibromododeeane,1-bromo-6-chlorohexane, 1-methylimidazole,N-Lithiotrifluoromethanesulfonimide, 2,2′-Azobisisobutyronitrile (AIBN),dichloromethane, ethyl acetate, and all test solutes were purchased fromAldrich (Milwaukee, Wis.). Untreated fused silica capillary tubing(0.25-mm inner diameter) and a fatty acid methyl ester (FAME) kitcontaining 19 standards was purchased from Supelco (Bellafonte, Pa.).Structures and physico-chemical properties of the monocation monomersand the dication crosslinkers used are shown in EXAMPLE A—Table A.Monomers 1, 2, and 3 were synthesized by reacting one molar equivalentof 1-vinylimidazole with a slight molar excess of 1-bromohexane,1-bromononane, and 1-bromododecane, respectively. These reactions wereperformed at room temperature in round bottom flasks lined with aluminumfoil to prevent thermal/photo-induced polymerization. Care should betaken when synthesizing and purifying these compounds to minimize excessheat/light during reaction or roto-evaporation to prevent unwantedreaction of the ionic liquid. The resulting bromide salt was evaporatedunder vacuum to remove the excess 1-bromoalkane. Three 15 mL aliquots ofethyl acetate were used to wash the ionic liquid to remove any otherimpurities. After evaporating the ethyl acetate under vacuum, thebromide salt was dissolved in water and mixed with one molar equivalentof N-Lithiotrifluoromethanesulfonimide, also dissolved in water. Afterstirring for 12 hours, the water was removed and the remaining ionicliquid thoroughly washed with water using three 50 mL aliquots of water.A portion of the third aliquot of water was subjected to the silvernitrate test to ensure the absence of silver bromide precipitate. Themonomers were then dried under vacuum and then placed under a P₂O₅vacuum in the absence of light.

The dication crosslinkers were synthesized using a modified procedurerecently reported for a series of geminal dicationic ionic liquids.Compound 4 in Table A is a mixture of C₆(vim)₂ ²⁺ (m/z=272.1), C₆vm(im)₂²⁺ (m/z=260.1), and C₆(mim)₂ ²⁺ (m/z=248.1) in a 1:2:1 molar mixture,respectively, as indicated in the electrospray mass spectrum in FIG. 4.When acquired in positive ion mode, the most dominant ions for thesethree structurally similar compounds appear to be the +1 ion minus aproton. Further experiments conducted in our group in which the C-2proton on the imidazolium ring (see FIG. 4 for numbering of ring system)is deuterated indicates that this proton is lost and causes one of thepositive charged aromatic rings to neutralize charge and give rise tothe +1 ion (data not shown). This mixture was synthesized by reactingone molar equivalent of 1-bromo-6-chlorohexane with one molar equivalentof 1-methylimidazole in an ice bath overnight. Subsequently, one molarequivalent of 1-vinylimidazole was added dropwise over a period of 30minutes and the temperature of the mixture increased to 55° C. for 3hours. Three 15 mL aliquots of ethyl acetate were used to extract anyexcess starting material and the bromide anion was exchanged for thebis[(trifluoromethane)sulfonyl]imide (NTf₂ ⁻) anion by reaction of twoequivalents of N-Lithiotrifluoromethanesulfonimide dissolved in waterfor every one equivalent of the crosslinker salt.

In an analogous manner, the remaining crosslinkers 5, 6, 7, and 8 wereprepared by reacting one molar equivalent of the dibromoalkane with twomolar equivalents of 1-vinylimidazole. Compound 9 was prepared byreacting one molar equivalent of 1-methylimidazole with molar equivalentof 1-bromononane at 100° C. for 5 hours. Clean-up and metathesisexchange for the NTf₂ ⁻ anion was performed as described above for thesynthesis of the monomer ionic liquids.

Capillaries were coated using the static coating method at 40° C.Coating solutions of the monomer and/or crosslinker ionic liquids wereprepared at concentrations of 0.20% (w/v) in dichloromethane. Prior toadding the dichloromethane to the monomer and/or crosslinker mixture,0.7 mg of AIBN (.about.3.5% by weight) was added. AIBN is known toundergo decomposition to form cyanoisopropyl radicals which subsequentlyproduce several products by dimerization, disproportionation reactions,or chain reactions. The thermal decomposition kinetics of AIBN have beenwell studied using a variety of spectroscopic and polarographictechniques. Based on an Arrhenius plot, Van Hook and co-workers haveproposed a rate expression for the decomposition of AIBN in solution tobe: k_(d)=1.58×0.10¹⁵ exp(−30.8 kcal./RT). For a temperature of 40° C.in which the capillaries are coated with the initiator present in thecoating solution, this yields a decomposition rate constant of.about.5.07×10⁻⁷ sec⁻¹. Due to the fact that this rate constant is sosmall and that the coating rate is relatively fast, there should be verylittle polymerization of the monomer/crosslinker mixture during thecoating of the capillary.

After coating, the ends of the capillary were flame sealed and thecapillary placed in a GC oven and heated from 40° C.-80° C. at 1°C./min. The capillary was then held at 80° C. for 5 hours to ensurecomplete polymerization. Helium carrier gas was then flushed through thecapillary at a rate of 1 mL/min and the capillary conditioned from 30°C. to 120° C. at 3° C./min and held at 120° C. for two hours.

Solvation thermodynamics can be determined chromatographically byrecognizing that the Gibbs free energy change, .ΔG°, of a solute betweenthe mobile phase and the stationary phase can be described by equation1:

$\begin{matrix}{{\Delta\; G\;{^\circ}} = {{- {RT}}\mspace{11mu}{\ln\left( \frac{k}{\Phi} \right)}}} & \lbrack 1\rbrack\end{matrix}$where k is the solute retention factor and Φ is the column phase ratio.An expression shown in equation 2 can then be derived and illustratesthe dependence of enthalpy, ΔH°, and entropy, ΔS°, on the change of theretention factor with temperature:

$\begin{matrix}{{\ln\mspace{11mu} k} = {{{- \left( \frac{\Delta\; H\;{^\circ}}{R} \right)}\frac{1}{T}} + \left\lbrack {\frac{\Delta\; S\;{^\circ}}{R} + {\ln\mspace{11mu}\Phi}} \right\rbrack}} & \lbrack 2\rbrack\end{matrix}$A van't Hoff plot of in k versus 1/T provides the entropy (intercept)and enthalpy (slope) and describes a solute's transfer from the gasphase to the ionic liquid stationary phase. In this work, the solvationthermodynamics were determined for seven different probe molecules,listed in EXAMPLE A—Table D, on two cross-linked ionic liquid phases andone ionic liquid stationary phase. As EXAMPLE A—Table D illustrates, theprobe molecules evaluated in this study differ in terms of size and thetypes of functional groups that they possess. For each probe molecule oneach stationary phase, three separate van't Hoff plots were constructedso that changes in the probe molecule retention factor could be used toprovide an error for each thermodynamic parameter. The probe moleculeretention factors were determined at six different temperatures toobtain the highest possible correlation coefficient (>0.989).

Previously we characterized a large number of room temperature ionicliquids in terms of multiple solvation interactions using the solvationparameter model, shown in equationlog k=c+rR ₂ +sπ ₂ ^(H) +aα ₂ ^(H) +bβ ₂ ^(H) +l log L ¹⁶  [3]This approach utilizes inverse gas-liquid chromatography and allows theuse of a large number of probe molecules to deconvolute solute retentionin terms of the type and magnitude of individual solvation interactions.The solute descriptors (R₂, π₂ ^(H), α₂ ^(H), .β₂ ^(H), log L¹⁶) fromEquation 3 are obtained from the literature for many probe moleculescontaining a variety of functional groups. The retention factor isdetermined chromatographically. The solute descriptors and retentionfactors are subjected to multiple linear regression analysis to obtainthe interaction parameter coefficients (r, s, a, b, l), which ultimatelycharacterize the stationary phase: r is the ability of the diionicliquid containing-stationary phase to interact with .π0 and n electronsof the solute, s is a measure of the dipolarity/polarizability of thediionic liquid containing-stationary phase, a defines the diionic liquidcontaining-stationary phase hydrogen bond basicity, b is a measure ofthe hydrogen bond acidity, and 1 refers to the ability of the diionicliquid containing-stationary phase to separate adjacent members of ahomologous series.

Test solutes used to determine interaction parameters and solvationthermodynamics were dissolved in dichloromethane. A Hewlett-Packardmodel 5890 gas chromatograph and a Hewlett-Packard 6890 seriesintegrator were used for all separations. Split injection and flameionization detection were utilized with injection and detectiontemperatures of 250° C. Helium was used as the carrier gas with a columninlet pressure of 3.1 psi and flow rate of 1.0 mL/min Methane was usedto determine the dead volume of the column. Multiple linear regressionanalysis and statistical calculations were performed using the programAnalyze-it (Microsoft).

Equation 4 can be used to approximate the stationary phase filmthickness for gas chromatographic capillaries coated by the staticcoating method,

$\begin{matrix}{d_{f} = \frac{d_{c} \times c}{400}} & \lbrack 4\rbrack\end{matrix}$where: d_(f) is the film thickness of the ionic liquid stationary phasein micrometers, d_(c) is the diameter of the capillary (in micrometers),and c is the percentage by weight concentration of the stationary phasedissolved in an appropriate solvent. FIG. 5 shows the effect of1-hexyl-3-vinylimidazolium bis[(trifluoromethane)sulfonyl]imidate filmthickness on the peak efficiency of naphthalene at 100° C. As the plotclearly demonstrates, the highest efficiency separations were carriedout with a film thickness of .about.0.07 μm (0.10% w/v of ionic liquidin dichloromethane) while the worst efficiency separations were obtainedon columns with a film thickness of .about.0.21 μm (0.33% w/v). In thiswork, all capillaries were coated with a 0.20% (w/v) coating solutionyielding a film thickness of approximately 0.125 μm.

Using the ionic liquids in EXAMPLE A Table A, a variety of free radicalcross-linking experiments were carried out in chloroform following themethod of Muldoon and co-workers.sup.48 to determine which ratios ofmonocationic/crosslinker monomers result in copolymers that possess theideal properties for a GC stationary phase. For example, some copolymers(i.e., formed from monomers 1 and 5) containing only a few percent byweight crosslinker resemble gum-like polysiloxane phases. However, otherhighly cross-linked copolymers formed hard plastics and are thereforeundesirable for gas-liquid chromatographic separations.

Monocationic monomer ionic liquids 1, 2, and 3 contain the1-vinylimidazolium cation with hexyl, nonyl, and dodecyl alkyl chains,respectively. When polymerized, these ionic liquids form linear polymerchains, as demonstrated previously by Marcilla and co-workers. Asillustrated in Table B, these stationary phases exhibited a range ofinitial separation efficiencies, ranging from 2813 plates/meter forionic liquid 1 and .about.1900 plates/meter for ionic liquid 3 whenconditioned to 120° C. While it appears that the hexyl substitutedvinylimidazolium cation produces a more efficient stationary phasecoating, subsequent evaluation of the stationary phases using higherconditioning temperatures revealed that the efficiencies of thesecapillaries decrease rapidly. After conditioning up to 350° C.,volatilization of the ionic liquids resulted in efficiencies thatdropped to several hundred plates/meter. No retention of naphthalene wasobserved after conditioning the capillaries to 380° C., indicating aninsufficient amount of ionic liquid remained on the capillary wall.

To produce a more thermally robust ionic liquid matrix, geminaldicationic vinylimidazolium crosslinkers with different length alkylchains separating the dications were mixed with the monocationicmonomers. These mixtures are shown in Table B under the heading“partially/fully crosslinked matrices.” From our previous solution-basedpolymerization experiments, it was found that the concentration ofcrosslinker is crucial for the formation of a matrix exhibiting idealstationary phase properties (data not shown). Compound 4 (see EXAMPLEA—Table A), is a mixture of three dicationic ionic liquids separated bya six carbon linkage chain. Electrospray mass spectrometry indicatedthat for every one of the 1,6-di(3-methylimidazolium)hexane[C₆(mim)₂ ²⁺]dications and 1,6-di(3-vinylimidazolium)hexane [C₆(vim)₂ ²⁺] dications,there are two of the1-(3-vinylimidazolium)-6-(3′-methylimidazolium)hexane [C₆vm(im)₂ ²⁺]dications. When a column was prepared by polymerizing/immobilizationonly this mixture, the initial efficiency after conditioning to 120° C.was nearly 3000 plates/meter (EXAMPLE A—Table B). Moreover, theefficiency dropped much less after conditioning the capillary at highertemperatures. For example, the efficiency of 4 after conditioning at350° C. was 1365 plates/meter whereas the efficiencies of themonocationic ionic liquids without crosslinker ranged from 120 to 197plates/meter after the same conditioning step. Clearly, by crosslinkingthe ionic liquids, the efficiency and thermal stability of thestationary phase is preserved at higher temperatures.

A series of different crosslinked ILs were also synthesized usingvarious ratios of 1-vinyl-3-hexylimidazoliumbis[(trifluoromethane)sulfonyl]imidate (1) and the dication mixture 4,described above. The highest efficiencies were obtained withcrosslinking mixtures formed with equal percentages of the monocationicand crosslinking monomers whereas copolymers formed with a higherconcentration of crosslinker exhibited lower efficiencies (see EXAMPLEA—Table B). The effect of the alkyl side chain of the monocationicmonomer was investigated by preparing equal molar ratios of thecrosslinking mixture 4 with two other monocationic monomers,1-vinyl-3-nonylimidazolium bis[(trifluoromethane)sulfonyl]imidate (2)and 1-vinyl-3-dodecylimidazolium bis[(trifluoromethane)sulfonyl]imidate(3). As Table B illustrates, there is very little difference betweenthese different composition crosslinked matrices in terms of separationefficiency and loss of efficiency at high temperatures. Recall thatpreviously it was noted that when the monocationic monomers werepolymerized without crosslinker, the length of the alkyl group appearedto have an effect on the separation efficiency/thermal stability of thestationary phase at higher temperatures. This demonstrates that thelength of the alkyl group on the monocationic monomer plays less of arole in the loss of separation efficiency at high temperatures when itis part of a crosslinked stationary phase.

Ionic liquid stationary phases based only on crosslinking monomers werealso evaluated. As shown in EXAMPLE A Table B, one mixture was based onthe crosslinking of vinylimidazolium dications separated by a nonanelinkage chain (0.20% 5) while the second mixture consisted of ionicliquids 5, 6, 7, and 8, namely dicationic ionic liquid monomersseparated by a nonane, decane, undecane, and dodecane linkage chain,respectively. This mixture of four crosslinkers, abbreviated asC₉₋₁₂(vim)₂-NTf₂ in EXAMPLE A—Table 4, was made due to the fact thatcompounds 6 and 8 are supercooled solids at room temperature and,therefore, are not ideal monomers for creating “gummy” or “waxy”stationary phases. This mixture consists of 10.88% by weight of 5, 9.29%of 6, 19.59% of 7, and 60.24% of 8.

A couple of interesting trends were observed for the highly crosslinkedionic liquid stationary phases that were not observed for themonocationic linear or partially crosslinked materials. First, althoughthe separation efficiency of the completely crosslinked stationaryphases was low after conditioning to 380° C., the ionic liquidstationary phase was still present as a thin film in the capillary whenviewed under microscope after prolonged exposure to this temperature. Incontrast, only a few partially crosslinked stationary phases (seeEXAMPLE A—Table B) provided retention of naphthalene after hightemperature conditioning. All stationary phases formed usingmonocationic monomers alone appeared to have decomposed and/orvolatilized completely from the capillary wall after conditioning to380° C.

The most impressive and interesting characteristic of the completelycrosslinked ionic liquid stationary phases is their apparent ability toexhibit a substantial increase in efficiency after conditioning at hightemperatures. Examples of this arc found in EXAMPLE A—Table B under theheading “Crosslinked Ionic Liquid Matrix.” In one such example, acrosslinked matrix previously described containing a mixture of fourdicationic crosslinkers, C₉₋₁₂(vim)₂-NTf₂ was formed and the efficiencyof this stationary phase was observed to undergo a 200%-250% increase inefficiency when the column was conditioned from 300° C. to 350° C. (seeEXAMPLE A—Table B). This trend was observed on all highly crosslinkedstationary phases examined and appears to be independent of the initialAIBN concentration in the coating solution (see EXAMPLE A—Table C).

The fact that the efficiencies of the highly crosslinked stationaryphases increase in this narrow temperature range is not well understood,but certainly makes them very useful for high temperature separations.Clearly, by exhibiting this behavior, these stationary phases appear toexhibit the smallest decrease in efficiency up to temperatures around350° C. For low to moderate temperature separations (25° C. to 285° C.),the partially crosslinked stationary phases, particularly thosecontaining equal weight percentages of ionic liquids 2 and 5, providethe highest efficiency separations up to 285° C. with little columnbleed at temperatures at and above 250° C. Meanwhile, the completelycrosslinked stationary phases provides the highest efficiencyseparations with little column bleed up to temperatures around 300°C.-380° C. Therefore, these two optimized types of immobilized ionicliquid stationary phases are specifically proposed for normal GCtemperature ranges and higher GC temperatures, respectively. Low tomoderate temperature separations are optimal with partial crosslinkingof the stationary phase whereas high temperature separations requiremore extensive crosslinking to maintain acceptable efficiency and lowcolumn bleed.

The two optimized crosslinked stationary phases chosen for the moderate(0.10% 2 and 0.10% 5) and high temperature (0.20% C₉₋₁₂(vim)₂-NTf₂)separations, were further studied to determine the effect of AIBNinitiator concentration on their separation efficiency and thermalstability. As shown in Table B, each copolymer was formed using adifferent concentration of AIBN in the coating solution. Theseconcentrations ranged from 10.0% (w/w of AIBN to ionic liquid) to 0.5%.For the partially crosslinked stationary phase, a higher weightpercentage of initiator results in a slightly more efficient stationaryphase (i.e., 3296 plates/meter for 0.5% AIBN to 3817 plates/meter for10.0% AIBN). In addition, the efficiencies of the 7.0% and 10.0% byweight initiator copolymers decrease less rapidly at higher temperatures(>250° C.) compared to those ionic liquid matrices produced with lowerinitiator concentrations. After the stationary phase is subjected to atemperature ramp up to 385° C., only the two copolymers formed with 7.0%and 10.0% initiator provide retention of naphthalene, however with verylow efficiency. The other two crosslinked stationary phases were nolonger observed in the capillary after high temperature conditioning(385° C.) and therefore provided no retention.

In the case of the highly crosslinked stationary phase (0.20%C₉₋₁₂(vim)₂-NTf₂), a nearly opposite trend to that observed for thepartially crosslinked ionic liquids was observed (EXAMPLE A—Table B).The efficiencies of the columns after the first conditioning step arehigher for the copolymers formed with lower AIBN concentration. However,it was still found that a higher weight percentage of AIBN results in asmaller decrease of efficiency at higher temperatures compared to thecopolymers formed with lower percentages of AIBN. All of the highlycrosslinked stationary phases were found to retain naphthalene afterconditioning at 385° C. As discussed previously, the highly crosslinkedstationary phases exhibit an increase in the separation efficiency fornaphthalene after being conditioned to 350° C. as compared to beingconditioned at only 300° C. The magnitude of this increase does notappear to be directly related to the initiator concentration. Forexample, the efficiency increase exhibited by the copolymer formed with3.5% AIBN is .about.171% higher after the 350° C. program compared tothe 300° C. program whereas that for the 10% AIBN is .about.250% higher.As previously observed for the partially crosslinked ionic liquids, theoverall decrease in efficiency is lowest for copolymers formed withhigher AIBN concentrations.

This indicates that at high temperatures the most efficient stationaryphases appear to be those that are crosslinked with a weight percentageof AIBN greater than 7.0%. In contrast, for lower/normal temperatureseparations, the choice of the monocationic monomer and crosslinkerplays a more important role in the stationary phase efficiency andhigher initiator concentration tends to prevent large decreases inefficiency with increasing temperature (see Table B).

It has been demonstrated previously that room temperature ionic liquidsact as broadly applicable, superb gas chromatographic stationary phasesin that they exhibit a dual nature retention behavior. Consequently,ionic liquid stationary phases have been shown to separate, with highefficiency, both polar and nonpolar molecules on a single column. Byproducing stationary phases that are either partially or highlycrosslinked, it is of interest to ensure that the solvationthermodynamics and solvation interactions inherent to ionic liquids arestill retained by their immobilized analogues.

The thermodynamics (Table D) and solvation interactions (EXAMPLE A—TableE) for the two optimized crosslinked and a neat ionic liquid weredetermined as previously described in the Experimental Section. As canbe seen from the data in these tables, both the free energy of transferof solute and particularly their interaction parameters are similar forboth the crosslinked and neat monomeric ionic liquid stationary phases.While the enthalpies of solvation for all probe molecules differed onlyslightly between the three ionic liquids, a larger difference wasobserved for the entropies of solvation on the highly crosslinkedstationary phase for certain solutes, i.e., 2-chloroaniline, ethylphenyl ether, and decane. The entropies of solvation were somewhat morenegative for these molecules indicating that they are part of a moreordered environment with the highly crosslinked stationary phase. Theseresults also indicate that solvation by these three ionic liquid-basedstationary phases has a substantial entropic component that contributesto large differences in solute free energy of transfer (see values for2-chloroaniline and decane in EXAMPLE A—Table D).

The solvation interaction parameters given in EXAMPLE A—Table E indicatethat the neat and two crosslinked ionic liquids are very similar interms of selectivity. All three stationary phases interact weakly vianonbonding and π-electrons (r-term). The hydrogen bond basicity (a) anddispersion forces (l) were the same within experimental error for allthree stationary phases. The partially crosslinked and neat ionicliquids possessed the same magnitude of dipolar interactions which weresomewhat lower than those exhibited by the highly crosslinked ionicliquid (see EXAMPLE A—Table E). Within experimental error, all threeionic liquids possessed the same ability to undergo hydrogen bondacidity (b) interactions.

The unique selectivity of ionic liquid stationary phases in theseparation of a wide variety of analyte molecules including alcohols,alkanes, polycyclic aromatic hydrocarbons (PAHs), polychlorinatedbiphenyls (PCBs), and chlorinated pesticides have been demonstrated. Thefact that the selectivity of the ionic liquid stationary phases ispreserved after crosslinking the matrix is demonstrated in FIG. 6 andFIG. 7. FIG. 6 shows a separation of 19 fatty acid methyl esters (FAMEs)on a 15 meter column coated with a partially crosslinked IL stationaryphase. This separation is performed in 12 minutes using the temperatureramp described. FIG. 7 illustrates the separation of a mixture of PAHsand chlorinated pesticides on a 12 meter highly crosslinked stationaryphase. The 9 minute, high temperature GC separation is carried out usinga temperature program up to 335° C. with little observed column bleed.While the selectivity of these ionic liquids is little different fromthat observed previously with the neat ionic liquids, the fact thatseparations can now be accomplished at higher temperatures with littlecolumn bleed, high efficiency, and little shifting of the retention timeafter exposure to extreme temperatures further demonstrates theeffectiveness of the immobilized ionic liquid.

This work addresses the fundamental issues relating to the use of ionicliquid stationary phases at high temperatures and column ruggedness.Specifically, it was demonstrated that by employing ionic liquidmonocationic monomers and dicationic crosslinkers, an immobilized GCstationary phase can be developed. The cross-linked stationary phasesretain the dual nature selectivity behavior inherent to all ionic liquidstationary phases. In addition, the columns can be used at hightemperatures with low column bleed while simultaneously providing highefficiency separations. Two types of stationary phases were identifiedin this work and differ in terms of their maximum/minimum operatingtemperatures. Partially crosslinked stationary phases are best forseparations conducted at temperatures from ambient to 280° C. while amostly crosslinked stationary phase is best suited for temperatures over300° C. While the moderate to high temperature range of the mostlycrosslinked stationary phase may overlap with the partially crosslinkedmatrix, lower efficiency separations were observed with the mostlycrosslinked stationary phase at low temperatures. Moreover, a dramaticincrease in efficiency of the mostly crosslinked stationary phase athigh temperatures further adds to its effectiveness and usefulness for avariety of applications in high temperature gas chromatography studies.

Of course, ionic liquids and in particular the diionic liquid salts ofthe present invention can be used in other separation and analyticaltechniques. Their range of applicability is in no way limited tochromatography. One technique in which these materials can be used inSolid Phase Extraction (“SPE”). In SPE, a sample contains an impurity orsome other element to be separated, identified and/or quantified. Thissample can be placed into a container in which diionic liquid salts ofthe present invention can be present in, and more broadly, ionic liquidsin an immobilized form. Ionic liquid materials can be bound(immobilized) to the walls of the container, adsorbed, absorbed onto abead or other structure so as to form a bead or other structure whichmay rest at the bottom of the container or be packed throughout thecontainer much as a liquid chromatography column can be packed withstationary phase. Alternatively, the ionic liquids and in particulardiionic liquid salts of the present invention can be immobilized bycross-linking or an analogous immobilization reaction as describedherein on some sort of other solid support such as a bead used inchromatography. These beads can also be placed at the bottom of, or canfill a container, much as a packed column used for liquidchromatography. Of course, the solid support can be any structure placedany where within the container.

In a particularly preferred embodiment, the container is actually asyringe where the ionic liquid and/or diionic liquid salts are affixedor disposed in one fashion or another at the base of the syringe, muchas a filter. When the needle of the syringe is placed in a sample andthe plunger is withdrawn, vacuum is formed drawing sample up into thebarrel of the syringe. This material would pass through at least onelayer of ionic liquid and, in particular, diionic liquid salts inaccordance with the present invention, which would bind at least one ofthe components of the liquid. The sample liquid could then be spilledout or the plunger depressed to eject it, the latter forcing the sampleback through the ionic liquid or diionic liquid salts positioned at thebottom of the barrel.

The liquid can be analyzed either for the presence of certain materialsor the absence of the material retained by the ionic liquid or diionicliquid salts of the present invention. Alternatively, the retainedmaterials can be removed (such as by placing the materials in adifferent solvent) or not and analyzed analytically by other means. Thesame technique may be used in a preparative fashion and/or as a means ofbulk purification as well.

Another technique in which immobilized ionic liquids and diionic liquidsalts of the present invention may be used is solid phasemicroextraction or SPME. Broadly speaking, in these techniques, aseparation material (in this case an ionic liquid or in particular adiionic liquid salt in accordance with the present invention) isabsorbed, adsorbed or immobilized in one way or another on a fibergenerally attached to a plunger in a microsyringe such as usually usedin gas chromatography. In the case of the invention, immobilized ionicliquids and absorbed, adsorbed and immobilized diionic liquid salts arecontemplated. The plunger is depressed, exposing the fiber and the fiberis then dipped into the sample of interest. The plunger can then bewithdrawn to pull the fiber back into the barrel of the syringe, or atleast the barrel of the needle for protection and transport. The syringecan then be injected through the septum of a gas chromatograph or someother device and the fiber thereby inserted into the column byredepressing the plunger of the microsyringe. The heat used in GC thenvolatilizes or otherwise drives the bound sample off where it is carriedby the mobile phase through the GC column, allowing for separationand/or identification. It can also be eluted by a liquid mobile phase inan HPLC injector or unbuffer capillary electrophoresis.

More specifically, solid phase microextraction is a technique in which asmall amount of extracting phase (in this case an ionic liquid andpreferably a diionic liquid salt in accordance with the presentinvention) is disposed on a solid support, which was then exposed to asample for a period of time. In situations where the sample is notstirred, a partitioning equilibrium between a sample matrix and theextraction phase is reached. In cases where convection is constant, ashort time pre-equilibrium extraction is realized and the amount ofanalyte extracted is related to time. Quantification can then beperformed based on the timed accumulation of analysis in the coating.These techniques are usually performed using open bed extractionconcepts such as by using coated fibers (e.g., fused silica similar tothat used in capillary GC or capillary electrophoresis, glass fibers,wires, metal or alloy fibers, beads, etc.), vessels, agitation mechanismdiscs and the like. However, in-tube approaches have also beendemonstrated. In-tube approaches require the extracting phase to becoated on the inner wall of the capillary and the sample containing theanalyte of interest is subject to the capillary and the analytes undergopartitioning to the extracting phase. Thus, material can be coated onthe inner wall of a needle, for example, and the needle injected withoutthe need for a separate solid support.

FIG. 8 shows an example of an SPME device (1). A stainless steelmicrotube 40 having an inside diameter slightly larger than the outsidediameter of, for example, a fuse silica rod 60 is used. Typically, thefirst 5 mm is removed from a 1.5 cm long fiber, which is then insertedinto the microtubing. High temperature epoxy glue is used to permanentlymount the fiber. Sample injection is then very much like standardsyringe injection. Movement of the plunger 30 allows exposure of thefiber 60 during extraction and desorption and its protection in theneedle 20 during storage and penetration of the septum. 10 shows thebarrel of the microsyringe, 50 shows the extreme end of the stainlesssteel microtube in which the silicon fiber is mounted. Another versionof a syringe useful for SPME in accordance with the present invention isillustrated in FIG. 9. Syringe 2 can be built from a short piece ofstainless steel microtubing 130 to hold the fiber. Another piece oflarger tubing 120 works as the needle. A septum 110 is used to seal theconnection between the microtubing 130 and the needle 120. The silicafiber 140 is exposed through one end of the microtubing 130 and theother end is blocked by a plunger 100. Withdrawing plunger 100 retractsmicrotubing 130 and the fiber 140 into the barrel of the device, theneedle 120. Depressing plunger 100 reverses this process. These are butexemplary structures and any syringe device, including those containinga needle or tube with the ionic liquid immobilized on the inner surfacethereof are also contemplated.

Any monoionic liquid or diionic liquid salt may be used in accordancewith the present invention. Diionic liquids such as those shownimmediately below can be absorbed or adsorbed onto a solid support aspreviously described.

In addition, ionic liquids, both monoionic and diionic liquid salts inaccordance with the present invention can be immobilized by being boundor cross-linked to themselves and to a solid support as previouslydiscussed in connection with manufacturing capillary GC columns. To doso, however, the species used should have at least one unsaturated groupdisposed to allow reaction resulting in immobilization. See for examplethe monocationic and dicationic species immediately below.

Another type of SPME technique is known as task specific SPME or TSSPME.Task specific SPME allows for the separation or removal, and thereforethe detection of particular species. These can include, for example,mercury and cadmium, although the technique is equally applicable toother materials. The concept is exactly the same as previously describedwith regard to SPME. However, in this instance, the ionic liquids ordiionic liquids used are further modified such that they willspecifically interact with a particular species. Those shown below, forexample, may be used in the detection of cadmium and mercury (Cd²⁺ orHg₂₊). The first monocationic material can be coated, absorbed oradsorbed onto a fiber as previously discussed. A diionic liquid salt canalso be absorbed or adsorbed in known fashion. The second and thirdionic liquid materials illustrated below, the first monoionic and thesecond dicationic, by virtue of the presence of unsaturated groups, canbe more easily immobilized on a solid support using techniques analogousto those described previously with regard to cross-linking in connectionwith manufacturing capillary GC columns.

Finally, a particular sample can be suspended in a matrix that includesionic liquids and preferably diionic liquid salts in accordance with thepresent invention. This matrix can be loaded or immobilized on the fiberof an SPME syringe as described above and then injected into a massspectrometer to practice a technique known as SPME/MALDI massspectrometry. The matrix is exposed to a UV laser. This causes thevolatilization or release of the sample much as heat does in a GC. Thisallows the sample to enter mass spectrometer where it can be analyzed.Ionic materials which can be used as a matrix include, withoutlimitation:

TABLE A Structure and physico-chemical properties of themonomers/crosslinkers used in this study Molecular Weight DensityRefractive # Ionic Liquid (g/mol) (g/cm³) Index 1

459.1 1.36 1.443 2

501.2 1.28 1.445 3

543.3 1.23 1.448 4

832.1 1.53 1.449

820.1

808.1 C₆(vim)₂-NTf₂:C₆vm(im)₂-NTf₂:C₆(mim)₂-NTf₂ 1:2:1 5

874.3 1.47 1.457 6

888.3 — — 7

902.3 1.44 1.457 8

916.3 1.42 1.458 9

489.3 1.30 1.434

TABLE B Effect of monomer structure and degree of crosslinking onstationary phase efficiency (theoretical plates/mater) as a function ofconditioning temperature. Partially Crosslinked Monocationic LinearIonic Liquid Matrix^(a) Ionic Liquid Polymers^(a) 0.10% 1 0.15% 1 0.05%1 0.10% 1 0.10% 2 0.20% 1 0.20% 2 0.20% 3 0.20% 4 0.10% 4 0.05% 4 0.15%4 0.10% 5 0.10% 4 30° C.-120° C. 2813 2429 1860 2926 2916 2714 1768 36602938 3° C./min Hold 2 hours 100° C.-200° C. 2415 2322 1694 2426 27692085 1679 3301 2775 3° C./min Hold 5 hours 150° C.-250° C. 2172 20261706 1945 2639 2156 1827 2743 2449 3° C./min Hold 3 hours 200° C.-285°C. 1778 1677 1100 1710 2180 2047 1623 2088 2302 3° C./min Hold 2 hours200° C.-300° C. 1542 1432 1090 1517 1835 1626 1226 1419 2058 3° C./minHold 1 hour 200° C.-350° C. 197 142 120 1365 417 433 719 1119 523 3°C./min Hold 1 hour 200° C.-380° C. — — — 193 — — — 291 — 3° C./min Hold20 min Crosslinked Partially Crosslinked Ionic Liquid Matrix^(a) IonicLiquid Matrix^(a) 0.10% 1 0.10% 2 0.10% 3 0.20% 0.10% 0.10% 5 0.10% 40.20% 5 C₉₋₁₂(vim)₂-NTf₂ C₉₋₁₂(vim)₂-NTf₂ 30° C.-120° C. 3566 2957 32063189 3155 3° C./min Hold 2 hours 100° C.-200° C. 3277 2872 3019 26342379 3° C./min Hold 5 hours 150° C.-250° C. 3016 2787 2469 1963 1598 3°C./min Hold 3 hours 200° C.-285° C. 2536 2361 1554 898 771 3° C./minHold 2 hours 200° C.-300° C. 2024 2157 1334 941 554 3° C./min Hold 1hour 200° C.-350° C. 146 340 2101 1891 950 3° C./min Hold 1 hour 200°C.-380° C. — — 503 269 239 3° C./min Hold 20 min ^(a)Ionic liquidpolymer formed using 3.5% AIBN

TABLE C Effect of AIBN initiator concentration on efficiency(theoretical plates/meter) as a function of conditioning of thecrosslinked stationary phase. The percentage of AIBN initiator indicatedis based on the weight percent of the ionic liquid. CrosslinkedPartially Crosslinked Ionic Liquid Matrix Ionic Liquid Matrix 0.20%0.20% 0.20% 0.20% 0.10% 2 0.10% 2 0.10% 2 0.10% 2 C₉₋₁₂(vim)₂-C₉₋₁₂(vim)₂- C₉₋₁₂(vim)₂- C₉₋₁₂(vim)₂- 0.10% 5 0.10% 5 0.10% 5 0.10% 5NTf₂ NTf₂ NTf₂ NTf₂ 0.5% AIBN 3.5% AIBN 7.0% AIBN 10.0% AIBN 0.5% AIBN3.5% AIBN 7.0% AIBN 10.0% AIBN 30° C.-120° C. 3296 3566 3831 3817 34263155 2792 2905 3° C./min Hold 2 hours 100° C.-200° C. 3215 3277 37033529 2697 2379 2275 2309 3° C./min Hold 5 hours 150° C.-250° C. 30903016 3069 3027 1723 1598 1682 1398 3° C./min Hold 3 hours 200° C.-285°C. 2210 2536 2375 2559 950 771 865 649 3° C./min Hold 2 hours 200°C.-300° C. 1317 2024 2298 2009 676 554 768 603 3° C./min Hold 1 hour200° C.-350° C. 112 146 598 1214 1593 950 1664 1506 3° C./min Hold 1hour 285° C.-385° C. — — 140 68 178 239 490 453 3° C./min Hold 20 min

TABLE D Comparison of solvation thermodynamics of one neat and twocrosslinked ionic liquids. Partially Crosslinked IL 0.10% nvim-NTf₂ (2)Mostly Crosslinked IL Temp. 0.10% C₉(vim)₂-NTf₂ (5) Neat Monomeric IL0.20% C₉₋₁₂(vim)₂-NTf₂ ^(a) Range 3.5% AIBN 0.20% nmim-NTf₂(9) 3.5% AIBN(° C.) ΔG ΔH_(AV) ΔS_(AV) ΔG ΔH_(AV) ΔS_(AV) ΔG ΔH_(AV) ΔS_(AV) ProbeMolecule Min Max (J/mol) (J/mol) (J/mol *K) (J/mol) (J/mol) (J/mol *K)(J/mol) (J/mol) (J/mol *K) Fluorophenol 40 100 −6071 −49308 ± −126 ±−6583 −48104 ± −121 ± −5429 −48323 ± −125 ± (70° C.) 31.0 2.3 (70° C.)79.5 0.25 (70° C.) 482.7 1.52 Naphthalene 40 100 −10087  −54353 ± −129 ±−10209  −53789 ± −127 ± −8902 −52825 ± −128 ± (70° C.) 23.7 0.67 (70°C.) 91.0 0.31 (70° C.) 52.3 0.15 2-Chloroaniline 40 100 −11320  −56616 ±−132 ± −11670  −57652 ± −134 ± −10064  −57075 ± −137 ± (70° C.) 18.10.06 (70° C.) 57.5 0.17 (70° C.) 63.4 0.21 Ethyl Phenyl 35 75 −7058−46482 ± −122 ± −7420 −46521 ± −121 ± −5622 −46662 ± −127 ± Ether (50°C.) 140 0.52 (50° C.) 69.0 0.21 (50° C.) 409 1.31 1-Octanol 35 75−10433  −59229 ± −151 ± −10481  −59277 ± −151 ± −8213 −56039 ± −148 ±(50° C.) 50.7 0.23 (50° C.) 58.2 0.44 (50° C.) 58.1 0.15 Decane 35 75−4457 −45497 ± −127 ± −4349 −45389 ± −127 ± −1813 −46408 ± −138 ± (50°C.) 363 1.5 (50° C.) 138 0.46 (50° C.) 98.7 3.52 Nitropropane 27 50−5220 −38808 ± −109 ± −5422 −39010 ± −109 ± −4367 −38263 ± −110 ± (35°C.) 49.5 0.17 (35° C.) 312 1.0 (35° C.) 198 0.60 ^(a)This mixtureconsists of a combination of a homologous series of ionic liquids thatare 10.88% by weight of 5, 9.29% of 6, 19.59% of 7, and 60.24% of 8.

TABLE E Comparison of interaction parameters of one neat and twocrosslinked ionic liquids. Interaction Parameters^(a) Temp (° C.) c r sa b l n R² F 0.20% nmim-NTf₂(9) 40 −2.98 0 1.62 1.91 0.36 0.75 32 0.99477.86 (0.11) (0.09) (0.10) (0.10) (0.13) (0.03) (0.10) 70 −3.05 0 1.541.57 0.18 0.63 32 0.99 660.78 (0.08) (0.07) (0.07) (0.07) (0.10) (0.02)(0.07) 100 −3.47 0 1.52 1.43 0.12 0.60 30 0.99 304.17 (0.11) (0.09)(0.10) (0.09) (0.13) (0.03) (0.09) 0.10% C₉(vim)-NTf₂ (2); 0.10%C₉(vim)₂-NTf₂ (5); 3.5% AIBN 40 −2.95 0 1.60 1.84 0.45 0.71 32 0.99404.82 (0.11) (0.10) (0.11) (0.10) (0.15) (0.03) (0.10) 70 −3.05 0 1.571.53 0.37 0.60 32 0.99 639.52 (0.08) (0.07) (0.08) (0.07) (0.10) (0.02)(0.07) 100 −3.49 0 1.54 1.41 0.31 0.54 30 0.98 299.60 (0.12) (0.09)(0.11) (0.09) (0.14) (0.03) (0.09) 0.20% C₉₋₁₂(vim)₂-NTf₂ ^(b); 3.5%AIBN 40 −3.31 0 1.92 1.94 0.59 0.68 32 0.99 573.26 (0.10) (0.09) (0.10)(0.09) (0.13) (0.03) (0.09) 70 −3.55 0 1.88 1.71 0.46 0.59 32 0.99305.25 (0.12) (0.10) (0.11) (0.09) (0.15) (0.03) (0.10) 100 −3.65 0 1.731.46 0.32 0.48 30 0.98 254.83 (0.13) (0.11) (0.13) (0.12) (0.18) (0.04)(0.11) ^(a)r = interaction via nonbonding and π-electrons, s =dipolarity/polarizability, a = hydrogen bond basicity, b = hydrogen bondacidity, l = dispersion forces, n = number of probe molecules subjectedto multiple linear regression analysis, R² = statistical correlationcoefficient, F = Fisher coefficient. Values in parenthesis are thestandard deviations for each interaction parameter. ^(b)This mixtureconsists of a combination of a homologous series of ionic liquids thatare 10.88% by weight of 5, 9.29% of 6, 19.59% of 7, and 60.24% of 8.

TABLE F Names of Compounds Found in Tables 1 and 2 C₃(mim)₂—Br1,3-di(3-methylimidazolium)propane di-bromide C₃(mim)₂—NTf₂1,3-di(3-methylimidazolium)propanedi-bis[(trifluoromethyl)sulfonyl]imidate C₃(mim)₂—BF₄1,3-di(3-methylimidazolium)propane di-tetrafluoroborate C₃(mim)₂—PF₆1,3-di(3-methylimidazolium)propane di-hexafluorophosphate C₆(mim)₂—Br1,6-di(3-methylimidazolium)hexane di-bromide C₆(mim)₂—NTf₂1,6-di(3-methylimidazolium)hexane di-bis[(trifluoromethyl)sulfonyl]imidaC₆(mim)₂—BF₄ 1,6-di(3-methylimidazolium)hexane di-tetrafluoroborateC₆(mim)₂—PF₆ 1,6-di(3-methylimidazolium)hexane di-hexafluorophosphateC₉(mim)₂—Br 1,9-di(3-methylimidazolium)nonane di-bromide C₉(mim)₂—NTf₂1,9-di(3-methylimidazolium)nonanedi-bis[(trifluoromethyl)sulfonyl]imidate C₉(mim)₂—BF₄1,9-di(3-methylimidazolium)nonane di-tetrafluoroborate C₉(mim)₂—PF₆1,9-di(3-methylimidazolium)nonane di-hexafluorophosphate C₁₂(mim)₂—Br1,12-di(3-methylimidazolium)dodecane di-bromide C₁₂(mim)₂—NTf₂1,12-di(3-methylimidazolium)dodecanedi-bis[(trifluoromethyl)sulfonyl]imidate C₁₂(mim)₂—BF₄1,12-di(3-methylimidazolium)dodecane di-tetrafluoroborate C₁₂(mim)₂—PF₆1,12-di(3-methylimidazolium)dodecane di-hexafluorophosphate C₉(bim)₂—Br1,9-di(3-butylimidazolium)nonane di-bromide C₉(bim)₂—NTf₂1,9-di(3-butylimidazolium)nonanedi-bis[(trifluoromethyl)sulfonyl]imidate C₉(bim)₂—BF₄1,9-di(3-butylimidazolium)nonane di-tetrafluoroborate C₉(bim)₂—PF₆1,9-di(3-butylimidazolium)nonane di-hexafluorophosphate C₃(m₂im)₂—Br1,3-di(2,3-dimethylimidaolium)propane di-bromide C₃(m₂im)₂—NTf₂1,3-di(2,3-dimethylimidazolium)propanedi-bis[(trifluoromethyl)sulfonyl]imidate C₃(m₂im)₂—PF₆1,3-di(2,3-dimethylimidazolium)propane di-hexafluorophosphateC₉(m₂im)₂—Br 1,9-di(2,3-dimethylimidazolium)nonane di-bromideC₉(m₂im)₂—NTf₂ 1,9-di(2,3-dimethylimidazolium)nonanedi-bis[(trifluoromethyl)sulfonyl]imidate C₉(m₂im)₂—BF₄1,9-di(2,3-dimethylimidazolium)nonane di-tetrafluoroborate C₉(m₂im)₂—PF₆1,9-di(2,3-dimethylimidazolium)nonane di-hexafluorophosphateC₁₂(benzim)₂—Br 1,12-di(3-benzylimidazolium)dodecane di-bromideC₁₂(benzim)₂—NTf₂ 1,12-di(3-benzylimidazolium)dodecanedi-bis[(trifluoromethyl)sulfonyl]imidate C₁₂(benzim)₂—PF₆1,12-di(3-benzylimidazolium)dodecane di-hexafluorophosphate C₃(mpy)₂—Br1,3-di(methylpyrrolidinium)propane di-bromide C₃(mpy)₂—NTf₂1,3-di(methylpyrrolidinium)propanedi-bis[(trifluoromethyl)sulfonyl]imidate C₃(mpy)₂—PF₆1,3-di(methylpyrrolidinium)propane di-hexafluorophosphate C₉(mpy)₂—Br1,9-di(methylpyrrolidinium)nonane di-bromide C₉(mpy)₂—NTf₂1,9-di(methylpyrrolidinium)nonanedi-bis[(trifluoromethyl)sulfonyl]imidate C₉(mpy)₂—PF₆1,9-di(methylpyrrolidinium)nonane di-hexafluorophosphate C₉(bpy)₂—Br1,9-di(butylpyrrolidinium)nonane di-bromide C₉(bpy)₂—NTf₂1,9-di(butylpyrrolidinium)nonane di-bis[(trifluoromethyl)sulfonyl]imidaC₉(bpy)₂—PF₆ 1,9-di(butylpyrrolidinium)nonane di-hexafluorophosphate

The invention provides a method of detecting a charged molecule having asingle charge (+1 or −1) using electrospray ionization-mass spectrometry(ESI-MS). In the method, a suitable amount of the diionic species of theinvention having the opposite charges of the molecule of interest isadded to the sample. The diionic species and the charged molecule form asalt complex. The salt complex is generally a solid. Because the diionicspecies has two charges, when complexed with the charged molecule, thecomplex has a net charge. The complex is then detected using ESI-MS. Theformation of the complex converts the charged molecule into an ionhaving a higher mass to charge ratio m/z, which can be transferred byESI more efficiently due to mass discrimination. The present inventionthus provides an ESI-MS method with substantially improved selectivityand sensitivity. Preferred is the use of dicationic species.

In one embodiment, the method of the invention includes selecting adiionic species that has a desired composition and structure, e.g.,desired charged group or a desired mass or a combination thereof. Thecharged group can be selected based on the composition and structure ofthe charged molecule to be detected. Preferably, the diionic species isspecific for the charged molecule to be detected. Thus, it is preferablethat the diionic species is such that it binds strongly with the chargedmolecule to be detected. More preferably, the charged group of thediionic species is such that it does not bind strongly with othercharged molecules different from the molecule of interest in the sample.Employing a diionic species that is specific for a charged molecule ofinterest allows high selectivity in detecting the charged molecule. Useof diionic species having two different ionic groups may offerparticular advantages in tailoring the affinities for differentmolecules for detection.

The mass of the diionic species is preferably selected to achieveoptimal detection by the mass spectrometer. In general, a diionicspecies having a large mass is used. The diionic species is preferablysuch that the complex has a m/z higher than 50. Most commercial singlequadrupole mass spectrometers are designed to have their optimumperformance at m/z values significantly higher than 100. In anotherpreferred embodiment, the diionic species is selected such that thecomplex has a m/z significantly higher than 100, e.g., at least about200, at least about 300, or at least about 400. A person skilled in theart will understand that the mass of the diionic species depends on thesizes of the charged groups as well as the bridging group. One or moreof these can be varied to obtain a diionic species of desired mass.

In another embodiment, the method of the invention includes selecting adiionic salt that dissociates with high yield. This can be achieved byselecting a diionic salt containing suitable counter ions. In caseswhere a diionic salt having desired ionic groups but less desirablecounter ions, it can be converted to a diionic salt containing thedesired counter ions by anion exchange. In a specific embodiment, afluoride salt is used, which, if not yet available, can be convertedfrom a dihalide, a bromide or an iodide salt by anion exchange.

In another embodiment, the method further includes a step of performingion chromatography prior to the addition of the diionic species.

Several dicationic species were used in detecting perchlorate (ClO₄ ⁻).In a preferred embodiment, the invention provides a method of detectinga charged molecule of −1 charge other than perchlorate (ClO₄ ⁻) by massspectrometry using a dicationic species of the invention. In anotherembodiment, the invention provides a method of detecting perchlorate(ClO₄ ⁻) by mass spectrometry using a dicationic species of theinvention which is not one of the dicationic species I-X. In stillanother embodiment, the invention provides a method of detecting acharged molecule of −1 charge by mass spectrometry using an“unsymmetric” dicationic species of the invention. In still anotherembodiment, the invention provides a method of detecting a chargedmolecule of −1 charge by mass spectrometry using a chiral dicationicspecies of the invention.

In another preferred embodiment, the invention provides a method ofdetecting a charged molecule of +1 charge by mass spectrometry using adianionic species of the invention. Any one of the dianionic speciesdescribed above can be used.

In still another preferred embodiment, the invention provides a methodof detecting a plurality of different charged molecules of +1 or −1charge by mass spectrometry using a plurality of different diionicspecies of the invention. Each of the diionic species is selected tospecifically bind one of the different charged molecules. Preferably,the different diionic species have different masses such that thecomplexes formed with their respective charged molecules can be detectedseparately.

Mass spectrometry can be carried out using standard procedures known inthe art.

In another aspect of the present invention, there are provided a mixturecomprising both the diionic liquid salts of the invention andtraditional stationary phase material such as but not limited topolysiloxanes, PEGs, methylpolysiloxances, phenyl substitutedmethylpolysiloxance, nitrile substituted methylpolysiloxance, carbowax.Such mixture (mixed stationary phase or “MSP”) can be used as stationaryphases in chromatography such as gas chromatography, liquidchromatography and high performance liquid chromatography as well as inSPE and SPME. Both dicationic salt and dianionic salt can be used forthis purpose. The MSPs can be non-cross-linked (e.g., absorbed oradsorbed on a solid support or column), can be “partially” cross-linkedor “more highly” cross-linked (i.e., immobilized on a solid support orcolumn) The diionic liquid salts may also be cross-linked or otherwisereacted with the traditional stationary phase material or merely mixedtherewith.

Thus, in one embodiment, the invention provides MSPs comprising at leastone of the diionic liquid salts of the invention and at least onetraditional stationary phase material at a suitable proportion.Appropriate combinations of the diionic liquid salt(s) and thetraditional stationary phase material(s) for producing the MSP is basedon the particular application as are the proportions of the diionicliquid salt(s) and the traditional stationary phase material(s) in theMSP. In a preferred embodiment, the ratio of the diionic liquid salt andthe traditional stationary phase material in the MSP is from about 1:9(i.e., about 10% of diionic liquid salt and 90% of traditionalstationary phase material) to about 9:1 (i.e., about 90% of diionicliquid salt and 10% of traditional stationary phase material), about 1:3(i.e., about 25% of diionic liquid salt and 75% of traditionalstationary phase material) to about 3:1 (i.e., about 75% of diionicliquid salt and 25% of traditional stationary phase material), about 1:2(i.e., about 33% of diionic liquid salt and 67% of traditionalstationary phase material) to about 2:1 (i.e., about 67% of diionicliquid salt and 33% of traditional stationary phase material), or about1:1 (i.e., about 50% of diionic liquid salt and 50% of traditionalstationary phase material) (w/w). Chromatography employing MSP mayperform better, e.g., having higher selectivity, than chromatographyemploying diionic liquid salts or the traditional stationary phasealone. As an example, an MSP comprising a simple mixture of about 67%(dibutyl imidazolium)₂(CH₂)₉ and 33% of methylpolysiloxance with 5%phenyl substitution was prepared and used to coat a column. This MSP wasshown to exhibit better separation of an essential oil. Cross-linkedversion of the MSP can also be used.

In addition, the invention also provides methods of preparing MSPs,solid supports and/or columns containing same, the MSPs, solid supports,syringes, tubes, pipettes tips, needles, vials, and columns themselves,and the use of columns and solid supports containing such MSPs inchromatography and other analytical or separation techniques such asthose described elsewhere herein.

Example A—Example 1

Compound #2

Synthesis of 2 involved adding 15.0 mL (0.148 mol) of 1,3-dibromopropanedropwise to 23.5 mL (0.295 mol) of 1-methylimidazole in a round bottomflask under constant stirring at room temperature. The reaction wascomplete within 2 hours. The bromide salt was dissolved in 100 mL waterand extracted with three 25 mL aliquots of ethyl acetate. Water wasremoved under vacuum heating and the remaining salt was dried under aP₂O₅ vacuum. Synthesis of the NTf₂ ⁻ salt consisted of dissolving 10grams (0.03 mol) of the bromide salt in 100-150 mL water. Two molarequivalents (0.06 mol, 3.92 grams) of N-lithiotrifluoromethylsulfonimidewere dissolved in 50 mL of water in a separate beaker and added directlyto the bromide salt. The solution was allowed to stir for 12 hours. Thetop water layer was removed to leave the ionic liquid. Three additional30 mL aliquots of water were added and extracted with the ionic liquiduntil the ionic liquid passed the silver nitrate test. The ionic liquidwas then dried using rotary evaporation and then further dried under aP₂O₅ vacuum.

Example A—Example 2

Compound #7

Synthesis of 7 involved adding 15.0 mL (0.098 mol) of 1,6-dibromohexanedropwise to 15.6 mL (0.196 mol) of 1-methylimidazole in a round bottomflask under constant stirring at room temperature. The reaction wascomplete within 2 hours. The bromide salt was dissolved in 100 mL waterand extracted with three 25 mL aliquots of ethyl acetate. Water wasremoved under vacuum heating and the remaining salt was dried under aP₂O₅ vacuum. Anions were exchanged by dissolving 10 grams (0.024 mol) ofthe bromide salt in .about.150 mL acetone. Two molar equivalents ofsodium tetrafluoroborate (0.049 mol, 5.38 grams) were then directlyadded to the acetone mixture. After allowing 24 hours for completemixing, sodium bromide was filtered off to leave the pure ionic liquid.The sample was then subjected to silver nitrate to ensure no silverbromide precipitate was present. Acetone was removed under vacuum andthe remaining ionic liquid dried under a P₂O₅ vacuum.

Example A—Example 3

Compound #17

Synthesis of 17 involved adding 15.0 mL (0.074 mol) of 1,9-dibromononanedropwise to 19.4 mL (0.148 mol) of 1-butylimidazole in a round bottomflask under constant stirring at room temperature. The reaction wascomplete after 5 hours. The resulting viscous liquid was dissolved in100 mL water and extracted with three 35 mL aliquots of ethyl acetate.Water was removed under vacuum heating and the remaining salt was driedunder a P₂O₅ vacuum.

Example A—Example 4

Compound #25

Synthesis of 25 involved dissolving 13.1 mL (0.148 mol) of1,2-dimethylimidazole in 125 mL 2-propanol and adding 15.0 mL (0.074mol) of 1,9-dibromononane dropwise in a round bottom flask equipped witha condenser and refluxing at 95° C. for 24 hours. After removal of2-propanol under vacuum, the bromide salt was dissolved in 100 mL waterand extracted with three 35 mL aliquots of ethyl acetate. Water wasremoved under vacuum heating and the remaining salt was dried under aP₂O₅ vacuum. Synthesis of the NTf₂ ⁻ salt consisted of dissolving 10grams (0.02 mol) of the bromide salt in 100-150 mL water. Two molarequivalents (0.04 mol, 11.48 grams) ofN-lithiotrifluoromethylsulfonimide were dissolved in 50 mL of water in aseparate beaker and added directly to the bromide salt. The solution wasallowed to stir for 12 hours. The top water layer was removed to leavethe ionic liquid. Three additional 30 mL aliquots of water were addedand extracted with the ionic liquid until the ionic liquid passed thesilver nitrate test. The ionic liquid was then dried using rotaryevaporation and then further dried under a P₂O₅ vacuum.

Example A—Example 5

Compound #29

Synthesis of 29 involved dissolving 25.0 g (0.158 mol) of1-benzylimidazole in 100 mL 2-propanol and adding 25.9 grams (0.079 mol)of 1,12-dibromododecane in a round bottom flask equipped with acondenser and refluxing at 95° C. for 24 hours. Due to thehydrophobicity of the salt, it was found to be quite insoluble in water.Therefore, it was washed with ethyl acetate (.about.75 mL) and thendried under P₂O₅. Because the bromide salt as not soluble in water, 10.0grams (0.016 mol) was dissolved in methanol with stirring. To anotherbeaker was added 8.9 grams (0.031 mol) ofN-lithiotrifluoromethylsulfonimide with approximately 50 mL of water.The two contents were mixed the mixture allowed to stir for nearly 5hours. The methanol-water solution was then removed and the liquidwashed with water and then further dried under vacuum and under P₂O₅.

Example A—Example 6

Compound #31

Synthesis of 31 involved dissolving 13.0 mL (0.128 mol) of1,3-dibromopropane in 100 mL 2-propanol and adding 26.6 mL (0.256 mol)of 1-methylpyrrolidine in a round bottom flask equipped with a condenserand refluxing at 95° C. for 24 hours. After removal of 2-propanol undervacuum, the bromide salt was dissolved in 100 mL water and extractedwith three 35 mL aliquots of ethyl acetate. Water was removed undervacuum heating and the remaining salt was dried under a P₂O₅ vacuum.

Example A—Example 7

Compound #35

Synthesis of 35 involved dissolving 12.0 mL (0.059 mol) of1,9-dibromononane in 100 mL 2-propanol and adding 12.3 mL (0.118 mol) of1-methylpyrrolidine in a round bottom flask equipped with a condenserand refluxing at 95° C. for 24 hours. After removal of 2-propanol undervacuum, the bromide salt was dissolved in 100 mL water and extractedwith three 35 mL aliquots of ethyl acetate. Water was P₂O₅ vacuum.Synthesis of the NTf₂ ⁻ salt consisted of dissolving 10 grams (0.02 mol)of the bromide salt in 100-150 mL water. Two molar equivalents (0.04mol, 11.48 grams) of N-lithiotrifluoromethylsulfonimide were dissolvedin 50 mL of water in a separate beaker and added directly to the bromidesalt. The solution was allowed to stir for 12 hours. The top water layerwas removed to leave the ionic liquid. Three additional 30 mL aliquotsof water were added and extracted with the ionic liquid until the ionicliquid passed the silver nitrate test. The ionic liquid was then driedusing rotary evaporation and then further dried under a P₂O₅ vacuum.

Example A—Example 8

Compound #38

Synthesis of 38 involved dissolving 13.0 mL (0.064 mol) of1,9-dibromononane in 100 mL 2-propanol and adding 20.0 mL (0.128 mol) of1-butylpyrrolidine in a round bottom flask equipped with a condenser andrefluxing at 95° C. for 24 hours. After removal of 2-propanol undervacuum, the bromide salt was dissolved in 100 mL water and extractedwith three 35 mL aliquots of ethyl acetate. Water was removed undervacuum heating and the remaining salt was dried under a P₂O₅.5 vacuum.Synthesis of the NTf₂ ⁻ salt consisted of dissolving 10 grams (0.019mol) of the bromide salt in 100-150 mL water. Two molar equivalents(0.037 mol, 10.62 grams) of N-lithiotrifluoromethylsulfonimide weredissolved in 50 mL of water in a separate beaker and added directly tothe bromide salt. The solution was allowed to stir for 12 hours. The topwater layer was removed to leave the ionic liquid. Three additional 30mL aliquots of water were added and extracted with the ionic liquiduntil the ionic liquid passed the silver nitrate test. The ionic liquidwas then dried using rotary evaporation and then further dried under aP₂O₅ vacuum.

Example A—Example 9

Procedure for the Synthesis of Di-Cationic Phosphonium ILs

1,10-decane-tripropyl phosphonium bromide

was synthesized according to the following procedure. The precedingionic liquid was synthesized according to the following procedure: In around bottom flask (100 mL), 1,10-dibromodecane (3.7 g) was dissolved inisopropyl alcohol (50-75 mL). At room temperature, tripropylphosphine(6.5 mL) was added to the solution. The resulting solution was stirredand heated under reflux for 48 hrs. After this time, the solution wascooled to room temperature. Rotoevaporation of the solvent followed bydrying in vacuum over phosphorous pentoxide, yielded a white crystallineproduct with a melting point of approximately 50° C.

Example A—Example 10

Synthesis of “Unsymmetric” Diionic Salts

The following compounds are used for the synthesis:

the alkyl linkage compounds:

the aryl linkage compounds:

the PEG linkage compounds:

The “unsymmetric” dicationic ILs are synthesized from dibromo-linkersaccording to the following steps:

First, the monocation intermediate is synthesized by reacting with thelinkage compound that is in excess during the reaction to decrease thesymmetric dicationic byproduct. For an example, the synthesis ofammonium-based monocation is shown in Scheme 1.

Then, the unsymmetrical diicationic ionic compound with the desiredanion is synthesized by the metathesis reaction from the dibromidecompound that is obtained as an example of ammonium-imidazonium based ILin Scheme 2.

Next, the unsymmetrical diicationic ILs are synthesized from the linkagecompound having both bromo- and hydroxyl-groups, shown as an example ofammonium-imidazonium based IL in Scheme 3.

Example B—Polymeric Ionic Liquids Example B—Example 1

A series of three homologous PILs are used to extract esters and fattyacid methyl esters (FAMEs) from aqueous solution. To examine the effectof the matrix on the coatings, extractions were carried out in asynthetic wine solution followed by recovery experiments in two realwine samples. The extraction performance of the PIL-based coatings iscompared to that of the commercial polydiinethylsiloxane (PDMS) andpolyacrylate (PA) coatings.

Materials.

The following analytes were purchased from Sigma Aldrich (Milwaukee,Wis., USA): hexyl tiglate, isopropyl butyrate, furfuryl octanoate, ethylvalerate, hexyl butyrate, benzyl butyrate, methyl caproate, methylenanthate, methyl caprylate, methyl octanoate, methyl decanoate, methylundecanoate, and methyl laurate.

Methanol, ethanol, hexane, dichloromethane, acetone, acetonitrile, andsodium hydroxide were obtained from Fisher Scientific (Fair Lawn, N.J.,USA).

The synthesis of all ionic liquid monomers and polymers involved the useof the following reagents, which were all obtained from Sigma-Aldrich(Milwaukee, Wis., USA): vinyl imidazole, 2,2′-azo-bis(isobutyronitrile),hexyl chloride, dodecyl bromide, and hexadecyl bromide. Lithiumbis(trifluoromethanesulfonyl)imide was obtained from SynQuest Labs(Alachua, Fla., USA).

Synthetic wine samples were prepared using (+)-tartaric acid purchasedfrom Sigma-Aldrich (Milwaukee, Wis., USA). Deuterated chloroform anddimethylsulfoxide were obtained from Cambridge Isotope Laboratories(Andover, Mass., USA). Deionized water (18.2 Megaohms/cm) was obtainedfrom a Milli-Q water purification system (Millipore, Bedford, Mass.,USA) and was used in the preparation of all aqueous solutions. Propaneand microflame brazing torches were purchased from Sigma-Aldrich(Milwaukee, Wis., USA).

The solid phase microextraction (SPME) devices were constructed using a5 μL syringe purchased from Hamilton (Reno, Nev., USA) and 0.10 mm I.D.fused silica capillary obtained from Supelco (Bellefonte, Pa., USA).Commercial SPME fibers of polydimethylsiloxane (PDMS, film thicknessesof 7 μm and 100 μm) and polyacrylate (PA, film thickness of 75 μm) wereobtained from Supelco (Bellefonte, Pa., USA). A fiber holder purchasedfrom the same manufacturer was used for manual injection of thecommercial fibers. Amber glass vials (20 mL) with PTFE/Butyl septa screwcaps supplied by Supelco (Bellefonte, Pa., USA) were used in the study.PTFE stir bars were obtained from Fisher Scientific (Fair Lawn, N.J.,USA) and were used to perform all extractions at a constant stirringrate of 900 rpm on a coming stir plate (Nagog Park Acton, Mass., USA).FIG. 16 is a non-limiting example of a system for headspace extraction.

Methods

An eight minute desorption time was used for all fibers. Analytecarryover (<1%) was periodically checked by reinserting the fiber intothe injector for an additional 5 minutes following the previousdesorption step. In all extractions, the volume of the aqueous solutionwas 15 mL. All analyses were carried out using an Agilent 6850N gaschromatograph (Agilent Technologies, Palo Alto, Calif., USA) equippedwith a flame ionization detector (FID). All separations were performedusing a DB-1 polydimethylsiloxane capillary column (30 m×0.32 mm I.D.,0.25 μm film thickness) purchased from Alltech (Deerfield, Ill., USA).

The following temperature program was used for the separation of theester mixture: initial temperature of 60° C. held for 3 min and thenincreased to 165° C. employing a ramp of 5° C./min. The carrier gas washelium with a flow rate of 1 mL/min Both GC injector and detectortemperatures were maintained at 250° C. using splitless injection, thedetector make-up flow of helium at 45 mL/min, the hydrogen flow at 40mL/min, and the air flow at 450 mL/min Agilent Chemstation software wasused for data acquisition.

Synthesis of Ionic Liquid Monomers and Polymers

Ionic liquid (IL) monomers and polymers (PIL) were synthesized using thereaction scheme shown in FIG. 10 and FIG. 11.

The three IL monomers (1-vinyl-3-hexyliinidazolium chloride,1-vinyl-3-dodecylimidazolium bromide, and 1-vinyl-3-hexadecylimidazoliumbromide) were produced by mixing 0.06 moles of 1-vinylimidazole with0.06 moles of the corresponding alkyl halide in −20 mL of 2-propanol.

The mixture was then allowed to react at 60° C. for 16 hours withconstant and vigorous stirring. After cooling to room temperature,2-propanol was evaporated under vacuum. The IL product was thendissolved in 20 mL of water and extracted five times with 10 mL portionsof ethyl acetate. Ethyl acetate was then removed under vacuum at 80° C.and the product was dried in a vacuum oven at 70° C. for two days. Thepurity was confirmed by IH-NMR before subjecting the monomer topolymerization.

Polymerization of the IL monomers (see FIG. 11) was carried out by freeradical polymerization. Briefly, 3.0 grams of the purified IL monomerwas dissolved completely in 30 mL of chloroform. To this mixture, 0.06grams (−2%) of the free radical initiator AIBN(2,2′-azo-bis(isobutyronitrile)) was added and refluxed for 3 hours at70° C. under an inert N₂ atmosphere. Chloroform was subsequently removedand the product dried under vacuum at 80° C. When needed, thepolymerization step was repeated until the peaks represented by thevinyl group in the IH-NMR disappeared.

FIG. 12 shows IH-NMR spectra of the 1-dodecyl-3-vinylimidazolium bromidemonomer and the corresponding poly(l-dodecyl-3vinylimidazolium) bromidepolymer. A comparison of the IH-NMR spectra of the PIL to that of the ILmonomer shows the disappearance of the double bond originating from thevinyl-substituted monomer (8=5.4 ppm, 5.9 ppm, and 7.3 ppm) and thebroadening of the signals due to hindered molecular tumbling. The halideanion was exchanged with the bis[(trifluoromethyl)sulfonyl]imide (NTf2)anion by metathesis anion exchange. Briefly, 0.10 moles of an aqueoussolution of lithium bis[(trifluoromethyl)sulfonyl]imide was mixed with0.10 moles of an aqueous solution of the polymerized IL and stirredovernight. The resulting product was filtered and extracted with three15 mL portions of water. The resulting IL polymer was dried under vacuumfor two days at 70° C.

All IL monomers and polymers were characterized using 1H-NMR and areavailable as supporting information. 1H-NMR [6/ppm relative to TMS]:

1-vinyl-3-hexylimidazolium chloride (400 MHz, d6-DMSO): 9.571 (s, 1H),8.219 1H), 7.947 (s, 1H), 7.298 (m, 1H), 5.950 (dd, 1H), 5.415 (dd, 1H),4.188 (t, 2H), 1.810 2H), 1.274 (m, 6H), 0.861 (m, 3H).

1-vinyl-3-dodecylimidazolium bromide (400 MHz, d6-DMSO): 9.532 (s, 1H),8.217 (s, 1H), 7.946 (s, 1H), 7.285 (m, 1H), 5.941 (dd, 1H), 5.427 (dd,1H), 4.184 (t, 2H), 1.807 (d, 2H), 1.181 (m, 20H), 0.846 (t, 3H).

1-vinyl-3-hexadecylimidazolium bromide (400 MHz, CDCl3): 10.961 (s, 1H),7.768 (s, 1H), 7.452 (m, 1H), 5.932 (dd, 2H), 5.378 (dd, 2H), 4.369 (t,2H), 1.915 (m, 4H), 1.258 (m, 32H), 0.855 (t, 3H).

Preparation of Ionic Liquid-Polymer Coated Fibers.

The SPME devices were constructed using a novel modification of theprocedure first described by Pawliszyn. The polyimide polymer wassubsequently removed from the last 1.0 cm segment of the fiber using ahigh temperature flame followed by sealing of the end of the capillaryusing a microflame torch. The fiber was then washed with methanol,hexane, acetone and dichloromethane followed by a 10 minute conditioningstep in the GC injection port at 250° C.

To make the PIL amendable to coating as a thin film on the fused silicafiber support, a solution was prepared by mixing the PIL in acetone at aratio of 9:1 (v/v). The conditioned bare fused silica fiber was dippedinto the PIL solution, held for 20 seconds, and removed from the coatingsolution and allowed to dry in the air for 10 minutes. Prior toperforming extractions, the coated fibers were conditioned at 250° C. inthe GC injection port for 10 minutes to eliminate residual solvents fromthe fiber support.

Headspace Extraction of Esters

Individual stock standard solutions of esters were prepared inHPLC-grade acetonitrile at a concentration of 1000 mg L⁻¹. Thesestandard solutions were stored at 4° C. and were used to prepare dailyaqueous working solutions containing a total acetonitrile content lowerthan 3% (v/v). All headspace extractions were carried out using 20 mLextraction vials containing 15.0 mL of the aqueous working solution. Thesorption-time profiles were obtained by extracting the studied analytesat a concentration of 200 μg L⁻¹ at varying extraction time intervalsusing a constant stir rate of 900 rpm at 23° C. The calibration curveswere obtained in Milli-Q water at an optimized extraction time of 50minutes with a total of at least 10 calibration concentrations.

To determine the effect of the matrix on the extraction of esters andFAMEs, extractions were performed in a synthetic wine sample as well asa red wine and white wine sample (Cranelake, Calif., USA). The syntheticwine solution was prepared according to a previously reportedformulation [25] by dissolving 3.5 g L⁻¹ of (+)-tartaric acid in ahydro-alcoholic solution (12% v/v ethanol) and using sodium hydroxide toadjust the pH to 3.5. The calibration curves of all synthetic winesamples were constructed using a 50 minute extraction time with a totalof 10 calibration levels. Analyte recovery experiments in the real winesamples were performed at two concentration levels, namely 100 μg L⁻¹and 400 μg L⁻¹.

Example B—Example 2

Development of Polymeric Ionic Liquid Coated Supports

Three PIL-based stationary phase coatings were evaluated. These PILsinclude: poly(ViHIm⁺ NTf₂ ⁻), poly(ViDDIm⁺ NTf₂ ⁻), and poly(ViHDIm⁺NTf₂ ⁻) and were synthesized by the free radical polymerization of1-vinyl-3-hexylimidazolium chloride, 1-vinyl-3-dodecylimidazoliumbromide, and 1-vinyl-3-hexadecylimidazolium bromide, respectively (seeFIG. 10-11).

The halogen anions were subsequently exchanged with thebis[(trifluoromethyl)sulfonyl]imide anion (NTf₂) in an effort toincrease the thermal stability of the PIL while also imparting morehydrophobic character to the stationary phase coating. The PILs werethen coated onto fused silica supports by dipping the fiber support intoa dilute solution of the PIL in acetone.

FIGS. 13A-13D show SEM photos of the bare fused silica fiber (FIG. 13A)and various angles of the fused silica fiber after coated with thepoly(ViHDIm⁺ NTf₂ ⁻) PIL (see FIGS. 13B-13D).

Using the PM-based coatings, the inventors herein obtained a smooth,homogeneous coating on the fiber (as opposed to neat ILs, which have atendency to form droplets on the surface of the fused silica support).Based on the SEM photos, the approximate film thickness of the PMcoating on the fiber is estimated to be approximately 12-18 μm.

To demonstrate that the PIL stationary phase is responsible for theextraction of the analytes examined, blank extractions using a 1.0 cmfused silica fiber containing no stationary phase were carried out on anaqueous solution of esters at a concentration of 500 μg L⁻¹. This data,not shown, revealed no appreciable extraction of analytes by the barefused silica support.

Extraction of Esters and Fatty Acid Methyl Esters (FAMEs) in Water.

Generation of Sorption-Time Profiles.

After initial conditioning of the PIL fibers, sorption-time profileswere obtained in an aqueous solution using headspace extraction.Throughout the construction of the sorption profile, the reproducibilityof the fiber was examined by performing triplicate extractions atvarious time intervals which yielded RSD values lower than 15%. Thesorption-time profile for the poly(ViHIm⁺ NTf₂ ⁻) coated fiber, shown inFIG. 14, were obtained by monitoring the area counts of each of theeleven analytes versus the fiber exposure time.

Equilibration was quickly reached in approximately 20 to 30 minutes formost analytes, except for a few longer chained FAMEs (e.g., methylundecanoate and methyl laurate), which attained equilibrium at longertimes Similar sorption-time profiles were obtained for the otherPIL-based coatings. Fifty minutes was selected as the optimizedextraction time of these analytes using all fibers for the entirecalibration study.

Analytical Performance.

Calibration curves were obtained for all three PIL-based coatings aswell as the PA and PDMS coatings in Milli-Q water.

The figures of merit including the sensitivity, detection limits, andcorrelation coefficients are shown in FIG. 21—EXAMPLE B Table 1 and FIG.22—EXAMPLE B—Example 1 Table 2, respectively.

The correlation coefficients varied between 0.986 and 0.999. It can beobserved from Table 1 (FIG. 21) that the sensitivity for a givenindividual analyte is nearly the same among the three PIL-based coatedfibers. The detection limits for most analytes using the PIL-basedfibers ranged between 2.5-50 4 g L⁻¹ where lower detection limits wereobtained for the larger FAMEs. Large increases in sensitivity wereobserved with increasing hydrophobicity of the analyte, particularly forthe homologous series of FAMEs.

For comparison purposes, Table 2 (FIG. 22) lists the calibration datafor three commercial SPME fibers. The two PDMS fibers contain filmthicknesses of 7 μm and 100 μm whereas the PA fiber contains of a 75 μmfilm thickness. Superior sensitivities and detection limits are observedwith the PDMS and PA fibers employing thicker absorbent coatings. Thesensitivities for most analytes are higher using the PIL-basedstationary phases (approximate film thickness of 12-18 μm) compared tothe PDMS coating employing a 7 μm film thickness, allowing for lowerdetection limits Despite the fact that the 75 μm PA fiber has a muchthicker film compared to the PIL fibers, similar sensitivities wereobtained for several analytes, particularly methyl undecanoate, methyllaurate, furfural octanoate, and hexyl tiglate.

A comparison of the sensitivity increase between methyl nonanoate andmethyl decanoate on the poly(ViHDIm⁺ NTf₂ ⁻) coated fiber revealed a325% increase in sensitivity compared to a 185% increase on the 100 μmPDMS fiber, 175% increase on the 7 μm PDMS fiber, and a 240% increase onthe 75 μm PA fiber.

These examples show that the hydrophobic nature of the PIL imparted bythe alkyl substituents on the imidazolium cation, along with thebis[(trifluoromethyl)sulfonyl]imide anion, provide solvationcharacteristics more similar to the PDMS coating rather than the PAcoating while often producing higher sensitivity and selectivity thanboth.

Evaluation of Matrix Effect.

The analyte distribution coefficient between the solution and fibercoating are dependent on the nature of the matrix [26]. To evaluate theeffect of matrix interference on the accuracy of the polymeric ionicliquid-based absorbent coatings, a calibration study of the esters andFAMEs was first carried out in synthetic wine. The primary advantage ofemploying a synthetic wine matrix is that the effect of ethanol contenton the observed extraction efficiency, selectivity, and sensitivity canall be studied independent of other volatile compounds that are widelypresent in all wines.

As shown in FIG. 23—EXAMPLE B—Table 3 and FIG. 24—EXAMPLE B—Table 4,respectively, the sensitivity decreased for all fibers when theextractions were carried out in a synthetic wine solution consisting ofapproximately 12% (v/v) of ethanol compared to when they were performedin Milli-Q water.

For the PIL-based coatings, the largest drop in sensitivity between thetwo matrices was observed for the smaller esters including isopropylbutyrate, ethyl valerate, and methyl caproate. Conversely, the 7 μm PDMSfiber exhibited the smallest sensitivity drop for these analytes. AllPIL-based fibers exhibited greater sensitivity with in the increase inthe alkyl chain of the FAME whereas, in general, a smaller enhancementin sensitivity was observed for the 7 micron PDMS fiber. Despite thematrix interference caused by ethanol, the detection limits of allPIL-based fibers were better than that of the 7 μm PDMS fiber.

To examine the effect of a real matrix, recovery studies were performedin both red and white wine samples. An extraction of both neat winesamples using two PDMS fibers (7 μm and 100 μm) and the three PIL fibersrevealed the concentration of all esters and FAMEs examined in thisstudy to be below the detection limit or absent from the sample. Usingthe calibration curves generated in the synthetic wine, recoveries weredetermined in triplicate at two spiking calibration levels, namely 100μg L⁻¹ and 400 L⁻¹.

As shown in FIG. 25—EXAMPLE B—Table 5, the precision of the red winesample using the PIL-based fibers was best at the higher spiking levelyielding RSD values below 12%. Due to the fact that the detection limitsfor most analytes in the synthetic wine samples ranged from 2.5-50 μgL⁻¹, it is understandable that the more complicated wine matrix wouldexhibit poorer repeatability.

Recoveries for the PIL-based fibers at the higher spiking level rangedfrom 70.2% for methyl laurate to 115.1% for ethyl valerate. Using the 7μm PDMS fiber, recoveries ranged from 61.9% for methyl laurate to 102.9%for isopropyl butyrate. The thicker PDMS coating (100 μm) yieldedrecoveries ranging from 74.4% for methyl laurate to 96.9% for methylenanthate.

FIG. 14 shows the chromatogram of the thirteen analytes obtained afterextracting a red wine sample spiked at 400 μg L-I using the poly(ViDDIm⁺NTf₂ ⁻) coated fiber.

Recovery and precision data for the white wine sample is shown in FIG.26—EXAMPLE B—Table 6. Recoveries for the PIL-based fibers at the higherspiking level ranged from 74.0% for ethyl valerate to 132.4% forfurfuryl octanoate with RSD values lower than 19.0%. For the 7 PDMSfiber, recoveries ranged from 48% for methyl laurate to 96.7% for methylcaproate with RSD values lower than 19.0%. The results clearly indicatethat the performance of the PIL-based fibers in terms of recovery andrepeatability is often superior to that of the PDMS fiber of similarfilm thickness.

FIGS. 17A-17D are graphs showing the quantitative analysis of esters andfatty acid methyl esters in red and white wines. FIGS. 17A-17C show thecalibration curves of 100 μm I.D. SPME fibers. FIG. 17D shows thecalibration curve of 50 μm I.D. SPME fiber.

FIG. 18 is a chart showing figures of merit for PIL-based extractions inwine.

Fiber Lifetime

The inventors also made polymeric ionic liquids that form stable, evenfibers while exhibiting superior thermal stability. Two of thePIL-coated fibers [poly(ViHIm⁺ NTf₂ ⁻) and poly(ViDDIm⁺ NTf₂ ⁻)] wereutilized in approximately 150 extractions while retaining RSD valueslower than 14-18%.

To attain high fiber lifetimes, care was taken during the fabrication ofthe fiber assembly, coating of the fiber, and the subsequentextraction/desorption steps, which make the fragile fused silicasusceptible to breakage. In certain embodiments, the structural designof the employed PIL may be important in achieving high thermalstability. Thus, in one particular embodiment, thebis[(trifluoromethyl)sulfonyl]imide salts paired with large, bulkycations can be used to produce IL monomers with exceptional thermalstability.

Further, in certain embodiments, it may be advantageous that the PIL befree of residual halides following anion metathesis as halides are knownto significantly lower the thermal stability of the product [13, 27]. Inaddition, in certain embodiments, it may be advantageous that thedesorption temperature and desorption time be optimized to prolong thelifetime of the coating material.

Example B—Example 3

Extraction of PTEXs

By polymerizing IL monomers to form polymeric ionic liquids (PILs),stable absorbent coatings were developed for the extraction of benzene,toluene, ethyl benzene, and xylenes in gasoline. The reproducibility andloading of the extraction phase has been improved by modifications tothe design of the SPME assembly.

FIGS. 19A-19C are graphs showing the quantitative analysis of PTEXcompounds in gasoline. FIG. 19A shows the sorption time profile. FIG.19B shows the calibration curves. FIG. 19C shows the gas chromatogram ofBTEX in gasoline. FIG. 20 is a chart showing the figures of merit forC16 PIL-based extraction in gasoline.

Example B—Example 4

Ionic Liquid-Based Absorbent Coatings for Microextractions

The use of ILs as absorbent coatings in solid phase microextraction(SPME) included the development of an extraction device employing afused silica support housed in a shielded syringe assembly. A method wasdeveloped to coat the IL on solid fused silica supports (˜1 cm inlength) by dipping the fiber in a solution of the IL in dichloromethane.The IL-coated fused silica support was then placed in the injection portof a GC at 200° C. for 4 minutes to completely remove the organicsolvent.

FIG. 27A and FIG. 27B show the fused silica support tip coated with ahighly viscous siloxy-based IL, whose structure is shown in the subset.

Sampling was performed by exposing the fiber to the headspace of anaqueous analyte solution for a pre-determined amount of time. Theanalytes were then desorbed, separated, and detected using GC. Initialattempts in coating the fused silica support indicated the desirably ofthe IL to exhibit two properties: (i) possession of a high viscositycapable of providing a stable, even coating on the solid support; and,(ii) possession of a high volatilization temperatures capable ofwithstanding the temperatures of the GC injection port (250-300° C.).

Despite the fact that high extraction efficiencies were obtained for avariety of polar and nonpolar analytes, the extraction to extractionreproducibility was poor with percent relative standard deviation (%RSD) values from 20-25%. The culprit for this loss in reproducibility islikely the substantial decrease in IL viscosity when exposed to the highinjection temperatures, thereby prompting the IL to flow off the fiberand into the injection port.

The inventors herein have now found that, in certain embodiments,improvements in the reproducibility can be attained by carrying out thedesorption step using lower injection temperatures (170-200° C.). Foranalytes in which higher injection temperatures (>200° C.) are required(i.e., analytes will low vapor pressures and high boiling points), thefiber can be re-coated after each extraction which produces typical %RSD values between 14-18%.

In addition to neat ILs, linear polymers of ILs have also been examinedas absorbent coatings. In one non-limiting example, the IL polymer issynthesized by free radical polymerization of the1-vinyl-3-alkylimidazolium bromide monomer using a free radical such asazobisisobutylonitrile (AIBN).

The extent of polymerization is monitored by 1H-NMR to ensure theabsence of any free monomers. The anion of the IL can be readilyexchanged through biphasic anion metathesis.

Polymerized ILs do not exhibit the same viscosity drop with elevatedtemperatures as their monomeric analogs. In addition, the polymers canbe easily dissolved in acetone and dip coated on the fused silica fiberto result in a thin film of the absorbent coating. The stability of thefilm (i.e., resistance to flowing) at elevated temperatures has resultedin % RSD values in the range of 3-12% and is highly analyte dependent.Typical % RSD values obtained in routine SPME are generally not higherthan 15%.

The gas chromatogram shown in FIG. 28 illustrates the headspaceextraction of a mixture containing 27 polar and nonpolar analytes froman aqueous solution using a polymerized IL fiber support, analogous tothat shown in FIG. 27. The structure of the IL polymer employed as theabsorbent coating is shown as the subset in FIG. 28.

Example B—Example 5

Ionic Liquid-Coated Supports

Using the IL-polymer coated support, it is now shown herein that adesorption temperature and time of 230° C. and four minutes,respectively, results in the amenability of the fiber to be used up toapproximately 65 extractions before the fiber becomes susceptible tobreakage or the % RSD values increase to over 15%. In addition,headspace extraction sorption time profiles have been measured foraliphatic hydrocarbons, fatty acid methyl esters, small-chained esters,and phthalate esters using both large sample volumes (e.g., 15 mLaqueous solution with ˜3.9 mL headspace) and small sample volumes (e.g.,600 μL aqueous solution with ˜400 μL headspace). Upon reaching theequilibrium time, calibration curves have been obtained for homologousmixtures of fatty acid methyl esters and small-chained esters.

FIG. 29—EXAMPLE B Table 7 shows the exceptional linearity of theanalytes studied. Also, additional classes of analytes includingpolyaromatic hydrocarbons and polychlorinated biphenyls can beextracted. The structure of the IL monomer was systematically modifiedthrough the incorporation of longer alkyl chains, aromatic moieties, andhydroxyl-functionality. Each IL-monomer is then paired with fourdifferent anions (e.g., Br—, NTf2-, PF6-, and BF4-) to show the cationand anion effects on extraction efficiency.

A structure/property relationship correlating the IL structure tosolvation characteristics can be conducted by examining IL andIL-polymer coated supports for two purposes: (i) to study thepartitioning of analytes between ILs and various solvents, and (ii) toutilize the unique and tunable solvation properties of the IL coatingfor the development of new microextraction absorbent coatings.

Using IL-based absorbent coatings, the solvation characteristics can becarefully chosen to selectively extract certain analytes from a complexmixture. For example, acidic analytes can be selectively extracted fromother analytes by utilizing an IL that possesses high hydrogen-bondbasicity. Likewise, aromatic analytes could be selectively extractedusing an IL capable of interacting strongly via π-π interactions.

Example B—Example 6

Ionic Liquid Coated Absorbents

A dip coating technique used to prepare the IL-coated supports issuccessful for ILs that possess high viscosities as they are less proneto flowing at high desorption temperatures. For less viscous ILs, the ILfilm can be re-coated after each extraction to restore the absorbentcoating. To investigate the effects of the IL cation and anion structureon overall analyte molecule partitioning, initial experiments ILs withthe different cation/anion combinations can be examined.

Representative structures of such traditional ILs are shown in FIGS.30A-30C in which the substituent groups on the 1, 2, and 3 positions ofthe imidazolium ring can be systematically varied to give rise to uniquecation structures. In addition, other cations such as pyridinium andpyrrolidinium can also be produced.

A variety of anions can be paired with given cations to show the effectof the anion on partitioning. The observed hydrogen bond basicity of ILsis largely a contribution from the anion whereas the hydrogen bondacidity appears to originate from the cation. Through modification ofaqueous solution pH, the extent of interaction between acidic and basiccompounds and various IL cations and anions can be shown.

Example B—Example 7

Immobilized Ionic Liquid Absorbents

The partitioning behavior of compounds to IL-polymers that are formed onthe surface of the solid support can be accomplished through thereaction of the free silanol groups on the surface of the fused silicasupport with a vinyl-terminated organoalkoxysilane. FIG. 31 shows thecoating and subsequent free radical reaction to form a thin,immobilized/crosslinked IP layer on a 1 cm segment of fused silica.

The vinyl-substituted IL monomers and/or crosslinkers can then be coatedon the support with AIBN and heated to induce free radicalpolymerization. In certain embodiments, the degree of crosslinking candictate the consistency of the formed polymer with lower degrees ofcrosslinker resulting in gel-like materials.

Extensive crosslinking may likely result in a more rigid, plastic-likecoating. The extent of crosslinking may influence the mechanism ofpartitioning (i.e., adsorption versus absorption) and the overallselectivity for targeted analyte molecules. In addition to thermallydesorbing analytes from the coating material in the injection port ofGC, these robust supports have the advantage of being adaptable tosolvent desorption in HPLC.

A solvent desorption device coupled to HPLC that accommodates theextraction devices can thus be used.

Example B—Example 8

Ionic Liquid Coated Stir Bar Supports

For analytes with low solubilities in aqueous solution or under verydilute conditions, a larger amount of IL may be required to achieve ameasurable partition coefficient.

FIG. 32 illustrates a procedure for producing thicker films ofimmobilized and coated ILs on glass stir bar supports. Following thecoating or immobilization procedure, the stir bar can be added directlyto the biphasic system, stirred, and then be retrieved tochromatographically determine the concentration of the analytes in theIL phase.

Due to the fact that the coating may be much thicker on the stir barsupport compared to that on the fused silica support, a thermaldesorption unit may be required to desorb analytes from the stir bar.The desorption unit utilizes cryogenic liquid nitrogen to focus theanalytes during the desorption step so that all analytes are subjectedto the head of the GC capillary column in one slug. For more refractorycompounds, HPLC can be used to separate and quantify the analytemolecules. This can be carried out by choosing the appropriate solventstrength of the mobile phase and either performing a back extraction orthe utilization of an existing solvent desorption chamber built into theinjection system.

Example B—Example 9

Determination of Partition Coefficients

FIGS. 33A-33B show examples of methods and appropriate equilibria thatcan be considered in determining the desired partition coefficients. Theequilibria are analogous to those derived previously for solid phasemicroextraction. The advantages of measuring partition coefficientsusing the proposed microextraction techniques are: (i) small volumes ofIL required to form the absorbent coating; (ii) an extensive range ofanalytes can be examined; (iii) identical analytes can be desorbed andseparated by both GC and HPLC allowing for a comparison of partitioncoefficients using two different desorption and separation methods; (iv)the proposed microextraction methods are faster than current shake-flaskmethods; and, (v) depending on the solvent properties of the IL and/orthe extent of crosslinking, the aqueous solution can be easily replacedby an organic solvent to form a biphasic system with the IL.

Example B—Example 10

Task-Specific Ionic Liquid (TSIL) Cation/Anion Structural Effects andExtraction Conditions to Analyte Partitioning

The unique solvation properties of ILs can be used to develop IL-basedextraction devices. TSILs represent a class of ILs in which the cationand/or anion incorporates unique functionality useful for enhancingdistinct interactions to perform desired tasks.

Use of TSILs.

A variety of TSILs, examples of which are can be synthesized. Forexample, the thioether, thiourea, and urea functionalized ILs (FIGS.34A-34C) are capable of selectively chelating Cd²⁺ and Hg²⁺. Absorbentcoatings of these neat ILs can be examined initially followed bysynthesis of their immobilized analogs Immobilization can take place onboth the fused silica and stir bar support. This can be accomplished byincorporating vinyl or allyl moieties into the 3 position of theimidazolium cation while retaining the task-specific functionality.

This method of measuring the partition coefficients can allow for theaddition of competing molecules in the biphasic system to determine anyconcentration limits that may affect the overall selectivity the TSILhas for target molecules. In addition, different IL anions can beexamined to probe the effect of the anion on the observed extractionefficiency of the metal ion. Other conditions such as aqueous solutiontemperature, pH, and electrolyte concentration can also be adjusted.

To detect and quantify pre-concentrated metal ions in the IL, a backextraction can be performed followed by detection using atomicabsorption spectrophotometry or inductively coupled plasma atomicemission spectrometry.

FIG. 35 shows a schematic illustration of on-fiber metathesis anionexchange using a partially crosslinked IL coating. The Cl⁻ anions (left)are being exchanged and replaced by PB₆ ⁻ (right).

Example B—Example 11

IL-Based CO₂ Selective Absorbent Coating

An intense area of research today lies with the development of newmaterials and methods for the sequestration of CO₂. Sequestration of CO₂is particularly important in the purification of sour natural gas,onboard naval submarines where clean air atmosphere is desired, and invarious industrial processes where scrubbers are typically employed.

TSILs can be designed to sequester CO₂ through the use of appendedamines to the cation core. The molar uptake of CO₂ per mole of TSILapproaches 0.5, demonstrating that the TSILs are sequestering CO₂ in ananalogous manner to the standard employed alkanolamines. The process ofCO₂ capture is reversible by heating the TSIL to temperatures around80-100° C.

Similar amine-functionalized TSILs can be used to form coated andimmobilized absorbent coatings for the development of task-specificmicroextraction devices. Following the extraction and capture of CO₂,the supports can be desorbed and separated using packed column GC with athermal conductivity or mass spectrometric detector. Using thisapproach, the following objectives can be met: (i) examination of TSILCO₂ selectivity in the presence of water vapor; (ii) effect oftemperature on CO₂ uptake into the TSIL; and (iii) influence ofpotential contaminating gases (e.g., H₂S, CO, COS) which may lengthenthe equilibrium uptake time of CO₂ into the TSIL. The task-specificextraction device can be incorporated into an industrial process for thedetection and quantification of CO₂ in gas streams.

BBIM-Taurate IL-Based CO₂ Selective Absorbent Coating

FIG. 36 shows the structure of -1butyl-3-butylimidazolium taurate(BBIM-taurate). FIG. 37 show a synthetic route for BBIM-taurate. FIG. 38is the gas chromatogram of BBIM-taurate.

BBIM-taurate IL was exposed to CO₂. FIG. 39 contains photographs showingBBIM-taurate before CO₂ exposure (right), and after (left) CO₂ exposure.The sorption data of BBIM-taurate (⋄) and BBIM-NTf₂ (□) is shown in FIG.40.

Materials

The synthesis of the ionic liquid monomers and polymers involved the useof the following reagents: vinyl imidazole, 1-bromohexane,2,2′-azo-bis(isobutyronitrile) (AIBN) and taurine, which were purchasedfrom Sigma-Aldrich (St. Louis, Mo., USA). Lithiumbis[(trifluoromethyl)sulfonyl]imide was obtained from SynQuest Labs(Alachua, Fla., USA). Deuterated chloroform and dimethylsulfoxide wereobtained from Cambridge Isotope Laboratories (Andover, Mass., USA).Deionized water (18.2 MΩ/cm) was obtained from a Milli-Qwater-purification system (Millipore, Bedford, Mass., USA). Ethylacetate, chloroform, 2-propanol, hexane, acetone, methanol, methylenechloride, and sodium hydroxide were obtained from Fisher Scientific(Fairlawn, N.J., USA). Propane and microflame brazing torches werepurchased from Sigma-Aldrich. Amberlite IRA-400(OH) ion-exchange resinwas obtained from Sigma-Aldrich.

All laboratory-made SPME devices were constructed using a 5-μL syringepurchased from Hamilton (Reno, Nev., USA) and 0.05 mm I.D. fused silicacapillary obtained from Supelco (Bellefonte, Pa., USA). Commercial SPMEfibers of PDMS (film thickness of 7 μm) and Carboxen™-PDMS (filmthickness of 75 μm) were obtained from Supelco. A fiber holder purchasedfrom the same manufacturer was used for manual injection of thecommercial fibers. Gas sampling bulbs (250 mL) with Thermogreen™ LB-1cylindrical septa were obtained from Supelco and used to perform CO₂extraction. A pressure gauge (0-±30 psi), obtained from FisherScientific, was used to record the pressure.

Synthesis of VHIM Ionic Liquids (IL) Monomers

The ionic liquid monomers were synthesized, as shown in FIG. 41.Briefly, 1-vinyl-3-hexylimidazolium bromide (VHIM-Br) was produced bymixing 1-vinylimidazole with an equimolar amount of 1-bromohexane in2-propanol. The mixture was then allowed to react at 60° C. underconstant stirring for 24 h. After removal of 2-propanol under vacuum,the product was dissolved in small amount of Milli-Q water and thenextracted with ethyl acetate five times to remove any unreacted startingmaterials. Ethyl acetate was then removed, and product was collected anddried in a vacuum oven. The purity of the VHIM-Br was confirmed by¹H-NMR before polymerization or metathesis anion exchange.

Synthesis of VHIM Ionic Liquids Polymers (PIL)

To obtainpoly(l-vinyl-3-hexylimidazolium)bis[(trifluoromethyl)sulfonyl]imide(poly(VHIM-NTf₂)), polymerization of VHIM-Br was carried out by freeradical polymerization, as shown in FIG. 42. Briefly, 5.0 g of thepurified VHIM-Br was dissolved in 30 mL of chloroform. Then, 0.1 g (˜2%)of the free radical initiator AIBN (2,2′-azo-bis(isobutyronitrile)) wasintroduced, and the solution was refluxed for 3 h under N₂ protection.Chloroform was then removed under vacuum and the product was dried in avacuum oven. The polymerization step was proved to be completed by thedisappearance of the peaks that represent the vinyl group in the ¹H-NMR.The polymerization was repeated when necessary. The obtainedpoly(l-vinyl-3-hexylimidazolium) bromide was dissolved in Milli-Q waterand equimolar amount of lithium bis[(trifluoromethyl)sulfonyl]imide(LiNTf₂) was introduced to this aqueous solution to perform metathesisanion exchange. This solution was stirred overnight, and the resultingpolymeric ionic liquid (PIL) precipitate, poly(VHIM-NTf₂), was collectedand washed with 3 aliquots of water and then dried under vacuum at 70°C. for 2 days.

Synthesis of Poly(VHIM-Taurate)

To synthesize poly(l-vinyl-3-hexylimidazolium) taurate, the counteranion of VHIM-Br was changed to hydroxide by passing the monomer througha column packed with ion-exchange resin in the hydroxide ion form, asshown in FIG. 43. Particularly, 100 mL of the regenerated ion-exchangeresin was packed into a 50×2 cm column followed by flushing excess 5 MNaOH to ensure the resin was completely switched to the hydroxide ionform. This was verified by adding silver nitrate to a collected fractionof the eluent. White silver bromide precipitate forms if bromide ionspersist in the solution. Nitric acid was used to avoid the potentialinterference of silver oxide, which is a dark precipitate and can bedissolved by introducing nitric acid. After regenerating the resincompletely, VHIM-Br was dissolved in water and passed through theion-exchange resin column with an appropriate flow rate.

The generated hydroxide-based IL was kept in aqueous solution, due toits limited stability. An acid-base titration was applied to determinethe concentration of the hydroxide-based IL in the aqueous solution. Thefinal step was a neutralization reaction between VHIM-OH and taurine. Anequimolar amount of taurine was dissolved in water and added into theVHIM-OH aqueous solution drop-by-drop to avoid intense reaction. Thereaction was completed overnight. Water was consequently removed byrotary evaporation, and the product was dried under vacuum for 48 h. NMRspectra were obtained to verify the structure of VHIM-taurate.Polymerization was performed using the aforementioned conditions toyield the poly(l-vinyl-3-hexylimidazolium) taurate [poly(VHIM-taurate)]PIL.

Preparation of PIL-Coated SPME Fibers

Laboratory-made SPME devices were constructed. Pre-treated SPME fiberswere coated with the poly(VHIM-NTf₂) PIL, poly(VHIM-taurate) PIL, aswell as mixtures containing these two PILs. To prepare a binary fibercoating mixture of PILs, poly(VHIM-NTf₂) and poly(VHIM-taurate) weremixed in chloroform at the desired weight percentages of each component.The coating solution was shaken for 5 min to ensure that the two PILswere homogeneously mixed. The film thickness of the PIL fibers coatingwere estimated by scanning electron microscopy.

Extraction of CO₂

The apparatus used is shown in FIG. 43. The operation of the SPME set-upwas performed according to the following steps:

(1) With the regulator closed, valve 1 and valve 2 were opened, and theentire system evacuated until the pressure reading from the pressuremeter was constant.

(2) Valve 1 was closed to isolate the system from the atmosphere. Theinitial pressure was recorded from the pressure gauge.

(3) The regulator was open to introduce the gas sample to the samplebulb. The reading from the pressure gauge was recorded as the finalpressure when the pressure reached a constant value.

(4) Valve 2 was closed and the SPME fiber exposed to the gas sampleinside the sample bulb for a desired length of time.

(5) The captured CO₂ was released from SPME fiber by high temperaturedesorption in the GC injection port, and the obtained CO₂ peak areanormalized by ΔP (final pressure−initial pressure).

GC Separation

All separation experiments were conducted using an Agilent Technologies6890N gas chromatograph (Agilent Technologies, Palo Alto, Calif., USA).The gas chromatograph is equipped with thermal conductivity and flameionization detectors coupled in series. All separations were performedusing a Carboxen™ 1010 PLOT capillary column (30 m×0.32 mm I.D.)purchased from Supelco. The following temperature program was used forthe separation of CO₂: initial temperature of 35° C. held for 10 min andthen increased to 225° C. employing a ramp of 12° C./min Helium was usedas the carrier gas with a flow rate of 1 mL/min. The inlet temperaturewas maintained at 250° C. for PDMS, Carboxen™-PDMS and poly(VHIM-NTf₂)PIL fibers, and 180° C. for the other fibers. A splitless injection wasused, and a purge flow to split vent of 20.0 mL/min at 0.10 min wasapplied. The thermal conductivity detectors were held at 250° C.,reference flow of 20.0 mL/min and the make-up flow of helium at 7.0mL/min Agilent Chemstation software was used for data acquisition.

FIG. 44: The gas chromatogram of the taurate-based IL.

FIG. 45: The gas chromatogram of the taurate-based PIL.

FIG. 46: Scanning electron micrograph of BBIM-taurate coated fiberbefore exposure to CO₂. FIG. 47A and FIG. 47B: Scanning electronmicrographs of same BBIM-taurate coated fiber after exposure to CO₂.

FIG. 48: Scanning electron micrograph of same BBIM-taurate coated fiberafter desorption.

FIG. 50: Sorption-time profile obtained under low pressure of CO₂showing the comparison of different IL-based sorbent coatings to 2commercial-based coatings (Carboxen and PDMS). The film thicknesses ofthe two commercial coatings are approximately six to seven times that ofthe IL-based systems.

FIG. 51: Sorption-time profile obtained under high pressure of CO₂showing the comparison of different IL-based sorbent coatings to 2commercial-based coatings (Carboxen and PDMS). The film thickness of thetwo commercial coatings are approximately six to seven times that of theIL-based systems.

FIG. 52: Sorption-time profile of CO₂ under medium pressure using theC₆-taurate based ionic liquid polymer.

FIG. 53: Chart showing relative standard deviation values demonstratingthe enhanced reproducibility of two IL-based polymer coatings comparedto two commercial-based sorbent coatings. The time in parenthesisrepresents the time during the extraction step in which the fiber waswithdrawn and subjected to GC analysis.

Example B—Example 12

Ion Exchange Mechanism in IL-Based Absorbent Coatings for the Tunabilityof Extraction Selectivity

Absorbent coatings comprised completely of ions have interestingproperties not observed with traditional SPME and SBSE coatingmaterials. The selectivity and utility of ILs can be realized byunderstanding the tunability offered by ion exchange processes.

Example B—Example 13

Selectivity Tuning by on-Support Anion Exchange

The cation and anion each contribute unique solvation interactionsthereby making ILs among the most complex solvents. In most traditionalimidazolium-based ILs, the anion provides the IL its hydrogen-bond basicbehavior. The synthesis of ILs can involve the construction of thecationic portion of the molecule followed by metathesis anion exchange.Using this approach, on-fiber metathesis exchange of anions fromimmobilized absorbents on both stir bar and fused silica supports can beproduced.

This method, shown schematically in FIG. 26, requires that the ILcoating be partially crosslinked to allow swelling of the polymer forcomplete metathesis exchange. This can be accomplished using a similarapproach that has been used for polymer beads resulting from partiallycrosslinking vinyl-functionalized IL monomers.

On-fiber anion exchange can allow for high throughput characterizationof IL-polymers as well as provide a simple route for altering theextraction selectivity of the absorbent coating.

Example B—Example 14

DNA Extractions Using Ionic Liquids

One of the most commonly employed methods of isolating and concentratingDNA and RNA from aqueous solution is the buffer-saturatedphenol/chloroform extraction system. Protein contaminants becomedenatured in the presence of the organic solvent and typically partitioninto the organic phase while the nucleic acid resides in the aqueousphase. Recently, the first ever extraction of DNA into the IL BMIM-PF₆(1-butyl-3-methylimidazolium hexafluorophosphate) was demonstrated where30% of the DNA could be back extracted into an aqueous buffered solutionusing a single stage extraction. It was also found that the IL usedpreferentially partitioned the nucleic acid over contaminating proteinsand metal species. Using NMR and IR, the interactions between thecationic BMIM⁺ and phosphate groups within the DNA acted to facilitatethe extraction into the IL.

The presently described support-assisted strategy of extracting analytesfrom solutions, can be used for the partitioning of double-stranded DNAinto PILs. For example, imidazolium-based PILs with thehexafluorophosphate and bis[(trifluoromethyl)sulfonyl]imide anions, canbe used since most of these PILs are water immiscible. The cationstructure can be varied using different lengths of alkyl chains on the 1and 3 positions of the imidazolium ring (see FIG. 30A) while maintainingliquids at room temperature.

Following extraction of the nucleic acids, the IL can be introduced intoan HPLC using a solvent desorption chamber.

The results obtained using the methods and ILs described herein are alsouseful in ion exchange mechanisms responsible for the extraction ofnucleic acids and can extend the realm of ionic liquids and separationscience into the mainstream of biology and biochemistry.

Example C—Determination of Volatility Example C—Example 1

Versatility of Ionic Liquids in Separation Science: Determination of LowVolatility Aliphatic Hydrocarbons and Fatty Acid Methyl Esters UsingHeadspace Solid-Phase Microextraction Coupled to Gas Chromatography

Static headspace-gas chromatography (HS-GC) is a common approach usedfor the analysis of analytes in the vapor phase that are in equilibriumwith a solid or liquid phase. In the sampling of less volatile analytes,it is often necessary to thermostat the liquid or solid phase atelevated temperatures, thereby increasing the equilibrium amount ofanalyte present in the headspace. However, heating of the sample oftencauses partial vaporization of the solvent, resulting in increasedpressure build-up within the sample vial. For that reason, it has beenstated that the vapor pressure of the extracting solvent dramaticallyaffects the enrichment factor achieved in HS-GC.

The inventors herein demonstrate the versatility of ILs in separationscience by introducing a HS-SPME-GC extraction/separation method inwhich carefully designed ILs are used as (1) a sample solvent forhydrocarbons and fatty acid methyl esters (FAMEs) possessing highboiling points (higher than 380° C.) and low vapor pressures, (2) highselectivity SPME sorbent coating for the HS extraction of analytes, and(3) low-bleed, high selectivity stationary phase for GC. Each IL hasbeen independently structurally engineered so that the imparted physicaland chemical properties are compatible with the requirements of eachcomponent of the method thereby producing a robust method in terms ofoverall analytical performance. To the inventors' knowledge, this is thefirst report in which these analytes have been successfully quantifiedby HS-GC.

Materials

The six analytes determined in this work were purchased fromSigma-Aldrich (Milwaukee, Wis., USA). Their molecular structures,boiling points, and vapor pressures are shown in EXAMPLE C—Table 1.

TABLE 1 EXAMPLE C Structures, boiling points, and vapor pressures of thehydrocarbons and fatty acid methyl esters evaluated in this study.Boiling Vapor Point(at Pressure Analyte Structure and Molecular Formula760 torr)^(a) (at 25° C.)^(a) Tricosane

380° C. 1.24 × 10⁻⁵ torr Hexacosane

412° C. 1.26 × 10⁻⁶ torr Triacontane

450° C. 7.37 × 10⁻⁸ torr Methyl heneicosanoate

387° C. 3.47 × 10⁻⁶ torr Methyl behenate

398° C. 1.52 × 10⁻⁶ torr Methyl tetracosanoate

420° C. 3.03 × 10⁻⁷ torr ^(a)Calculated using Advanced ChemistryDevelopment (ACD/Labs) Software V9.04 for Solaris.

PTFE stir bars (6 mm long) and silicone oil were obtained from FisherScientific (Fair Lawn, N.J., USA). Untreated fused silica capillarytubing (0.25 mm I.D.) and glass vials (2 mL) with PTFE septa caps werepurchased from Supelco (Bellefonte, Pa., USA). A model 324 directimmersion heater was purchased from Cole Parmer (Vernon Hills, Ill.,USA) and a model Arrow 6000 overhead stirrer was obtained from ArrowEngineering Co., Inc. (Hillside, N.J., USA). A Cimarec magnetic stirrerwas acquired from Barnstead Thermolyne (Dubuque, Iowa, USA). The IL1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate[HMIM] [FAP] was provided by Merck KGaA (Darmstadt, Germany). Themolecular structure of this IL is shown in FIG. 52.

Methods

The coating of the GC column with the high stability IL was performedusing the static method on a fifteen-meter capillary column (0.25 mmI.D.). The coating method utilized a 0.25% (w/v) solution of thedicationic IL 1,12-Di-(3-butylimidazolium)dodecanebis[(trifluoromethyl)sulfonyl]imide [C₁₂(BIM)₂] [NTf₂] (shown in FIG.52) in methylene chloride at 40° C. The synthesis of this dicationic ILwas carried out. Coated capillaries were conditioned overnight from 40°C. to 100° C. at 1° C.·min⁻¹ using a constant flow of helium at a flowrate of 1.0 mL·min⁻¹ Column efficiency was tested with naphthalene at120° C. The column possessed an efficiency of 1554 plates·m⁻¹ at 120°C., and was tested weekly to ensure that the efficiency remainedconstant.

All GC experiments were conducted using an Agilent Technologies 6890Ngas chromatograph (Palo Alto, Calif., USA). The gas chromatograph wasequipped with thermal conductivity (TCD) and flame ionization (FID)detectors coupled in series. Helium was used as the carrier gas with aflow rate of 1 mL·min⁻¹. The inlet and detector temperatures wereoperated at 250° C. Splitless injection was used during all experiments.The make-up flow of helium was maintained at 45 mL·min⁻¹, the hydrogenflow at 40 mL·min⁻¹, and the air flow at 450 mL·min⁻¹ The followingtemperature program was used in the separation of the analytes: theinitial temperature of 150° C. was held for 4 minutes, then raised to160° C. at a ramp of 10° C.·min′ and held for 2 minutes, and then raisedto 170° C. at a speed of 10° C.·min⁻¹ and held for 5 minutes.Afterwards, a 10° C.·min⁻¹ ramp was used to increase the oventemperature to 180° C. and was held for another 5 minutes. Finally, thetemperature of the oven was raised to 195° C. using a ramp of 15°C.·min⁻¹ and was held for 15 minutes. Agilent ChemStation software wasused for data acquisition.

The preparation of the PIL-based SPME coating involved the synthesis ofthe poly[ViHDIM] [NTf₂] PIL (see structure in FIG. 52) followed by thepreparation of fibers. The film thickness of the coating was in therange of 10-15 μm, as estimated by optical microscopy. The desorptiontime for the fiber in the GC injector was fixed at 5 minutes in allexperiments.

A stock solution was prepared by dissolving 2 mg of each of the analytesinto 40 g of the [HMIM] [FAP] IL, which was dried in a vacuum oven at70° C. overnight before use. The stock solution was maintained atapproximately 60° C. in order to ensure a homogenous mixture. Theworking solution was prepared by diluting different amounts of the stocksolution with pure [HMIM] [FAP] to various concentrations. The totalmass of the working solution was maintained at 400 mg in the sample vialand the volume of the headspace was 1.5 mL for all extractions. Thesorption-time profiles were obtained by immersion of the PIL coatedfiber into the headspace of the working standard solution containing thestudied analytes at a concentration of 25 mg of analyte per kg of [HMIM][FAP], using different extraction times (from 15 to 150 min) whilestirring at 170±10° C.

FIG. 53 shows a detailed schematic of the extraction and separationsystem utilized. Static headspace extractions were performed by firstpiercing the sampling vial containing the IL/analyte mixture and stirbar with the syringe housing the SPME fiber. The sampling vial was thenpositioned in the heated silicone oil bath followed by stirring of theIL/analyte mixture using a magnetic stirrer. The SPME fiber was thenexposed to the headspace of the sampling mixture. In order to minimizelarge temperature variations throughout the extraction, an overheadmechanical stirrer was used to stir the oil bath. Following theextraction, the SPME fiber was withdrawn into the syringe, the syringeremoved from the vial, and the fiber thermally desorbed in the GCinjector thereby subjecting the analytes to the IL-based stationaryphase for separation.

Results and Discussion

Component 1: [HMIM] [FAP] IL as Thermally Stable Solvent for HighTemperature Extraction

To function as an effective solvent in headspace extraction studies, anIL should possess the following features: (1) be chemically unreactivewith analytes being examined, (2) exhibit high thermal stability, (3)ability to dissolve the analytes in the concentration range needed formaking adequate calibration curves, and (4) exhibit reasonably lowviscosity to facilitate the preparation of samples and standards as wellas to ensure efficient sample agitation during extraction. Merck KGaAhas recently developed a class of hydrophobic ILs that exhibit muchlower water uptake than commonly studied NTf₂ ⁻ andhexafluorophosphate-based ILs. ILs containing this unique anion exhibitviscosities comparable to the NTf₂ ⁻ anions. Thermal gravimetricanalysis of this class of ILs has revealed that imidazolium-based ILsdecompose at temperatures above 280° C. The solubility of the analytesin the [HMIM] [FAP] IL was found to be acceptable in the range up to 50mg of analyte per kg of IL.

Component 2: Poly[ViHDIM] [NTf₂] PIL as SPME Sorbent Coating forSelective Headspace Extraction of Analytes

The polymeric nature of PIL compounds provides them additional thermalstability as well as exceptional film stability, thereby producing highextraction-to-extraction reproducibility and lifetimes comparable tocommercially coated fibers. The selectivity of PIL-based coatings can bemodulated by introducing functional groups to the cationic portion ofthe IL or by incorporating different anions to impart desired solventcharacteristics.

The poly[ViHDIM] [NTf₂] PIL was chosen in the Example as it undergoesstronger dispersion-type interactions with the analytes thus producinghigh extraction efficiencies.

Component 3: [C₁₂(BIM)₂] [NTf₂] IL as Highly Selective and Low-Bleed GCStationary Phase

ILs have been shown to be highly selective stationary phases for GC. Tofulfill the requirements of this component for this study, a relativelynonpolar stationary phase possessing low bleed at elevated temperatureswas required. The dicationic IL [C₁₂(BIM)₂][NTf₂] was chosen as it hasbeen shown previously to exhibit high thermal stability, a wide liquidrange, and broader selectivities compared to many traditional classes ofmonocationic ILs.

Synergy of Three IL-Based Components in Extraction/Separation System

The analytes extracted in this work include three hydrocarbons:tricosane, hexacosane, and triacontane; and three fatty acid methylesters: methyl behenate, methyl heneicosanoate, and methyltetracosanoate. These analytes were dissolved in the [HMIM] [FAP] IL andthen extracted by HS-SPME-GC. In order to achieve adequate extractionefficiencies using the HS-SPME method, high temperature is required forthese less volatile analytes. However, the sorption of the analytes tothe SPME coating is an exothermic process, and as the temperatureincreases, the analyte to coating partition coefficient decreases.Therefore, the temperature must be optimized so that the decrease of thepartition coefficient is offset by the increase in the equilibriumconcentration of the analytes in the headspace to achieve reasonableextraction efficiencies. The optimized extraction temperature was170±10° C. The extraction time and temperature in several previouslyreported studies involving headspace applications for less volatileanalytes (with by ranging from 152 to 228° C.) are: 10 minutes at 110°C., 15 minutes at 100° C., and 15 minutes at 150 or 180° C., dependingon the analyte.

Sorption-time profiles were generated by performing the extraction atvarious time intervals to identify the equilibration time using theoptimum temperature. FIG. 54 shows the sorption-time profiles obtainedby plotting the analyte peak area versus the extraction time. Tricosaneand hexacosane reach equilibrium at around 60 minutes whereas theremaining analytes reach equilibrium in around 100 min. An extractiontime of 100 min was considered as the optimum extraction time. Thecomparison of the extraction efficiencies for the hydrocarbons and FAMEscan also be observed in FIG. 54. With respect to the hydrocarbons, thelightest hydrocarbon (tricosane) exhibits the highest extractionefficiency whereas the lowest extraction efficiency is seen with theheaviest hydrocarbon, triacontane. The same trend is observed with thethree FAMEs, although their extraction efficiencies are much lowercompared to the studied hydrocarbons. The trend in the extractionefficiency is consistent with the vapor pressures and boiling points ofthese analytes (see EXAMPLE C Table 1).

Example C—Example 2

Analytical Performance of the Method

Calibration curves were obtained using working standard solutions ofanalytes in the [HMIM] [FAP] IL at different concentrations whileperforming the extraction at the optimum extraction time andtemperature. The figures of merit for the entire method, shown inEXAMPLE C Table 2, include the sensitivity, calibration range,correlation coefficients, error of the estimate, and limits ofdetection.

EXAMPLE C TABLE 2 FIGURES of merit of the calibration curves for theoverall method using a three component extraction and separation systemcomprised of ionic liquids. Calibration range Error of the LOD^(b)Analyte (mg · kg⁻¹) Slope ± SD^(a) estimate R (mg · kg⁻¹) Tricosane 1-45137.7 ± 3.4  164 0.998 0.1 Hexacosane 1-35 123.4 ± 4.6  151 0.996 0.2Triacontane 1-30 36.8 ± 2.2 36.3 0.993 0.3 Methyl behenate 2-30 25.9 ±0.5 28.3 0.998 0.4 Methyl 1-45 13.4 ± 0.7 14.7 0.994 0.4 heneicosanoateMethyl 2-45 12.6 ± 0.7 29.6 0.990 0.6 tetracosanoate ^(a)SD: error ofthe slope for n = 8 calibration levels. ^(b)LOD: limits of detectionscalculated as three times the signal to noise ratio.

The obtained linearity of the overall method was found to be acceptable,with correlation coefficients (R) ranging from 0.990 to 0.998. Thesensitivity, which can be evaluated by the slope, is higher for thehydrocarbons, particularly for tricosane, than for the FAMEs. It can beclearly observed that the sensitivity decreased with increasing carbonchain length of the hydrocarbons and FAMEs. The limits of detectionvaried from 0.1 mg·kg⁻¹ for tricosane to 0.6 mg·kg⁻¹ for methyltetracosanoate. This constitutes the first report of a headspaceextraction approach for these particular analytes. However, otheranalytes possessing high boiling points have been determined previouslyby headspace extraction. They include N,N-dimethylformamide (DMF),N-methyl-2-pyrrolidine (NPM), propylene glycol (PG), formamide,tri-n-butylamine (tBA), and 2-ethylhexanoic acid (2EHA). The boilingpoints for these analytes are in the range 152-228° C. and the reporteddetection limits for these analytes are 53 mg·L⁻¹ or 1-90 mg·L⁻¹depending on the IL solvent for DMF; 2.5 mg·L⁻¹ or 1-100 mg·L⁻¹depending on IL solvent for NMP; 13 mg·L⁻¹ for formamide; 8 mg·L⁻¹ fortBA; and 22 mg·L⁻¹ for 2EHA. For comparison, the analytes determined inthis method possess boiling points in the range 380-450° C. withdetection limits less than 0.6 mg·kg⁻¹.

The reproducibility of the method was evaluated by carrying out a seriesof extractions using working standard solutions of the analytes at twodifferent concentration levels, namely, 4 and 20 mg of analyte per kg of[HMIM] [FAP] IL. The obtained results can be observed in EXAMPLE C—Table3.

EXAMPLE C TABLE 3 Precision and extraction efficiency at differentspiking levels for the overall method. Spiking level: Spiking level: 4mg · kg⁻¹ 20 mg · kg⁻¹ Analyte RSD^(a) (%) RR^(b) (%) RSD^(a) (%) RR^(b)(%) Tricosane 15 99.1 10 75.9 Hexacosane 18 78.5 5.9 69.9 Triacontane 21114 16 103 Methyl behenate 22 121 15 98.3 Methyl heneicosanoate 21 11516 78.3 Methyl tetracosanoate 11 122 6.9 106 ^(a)RSD: relative standarddeviation for n = 4. ^(b)RR: relative recovery for n = 4.

The relative standard deviation ranged from 11 to 22% for the lowerspiking level (4 mg·kg⁻¹), and from 5.9 to 16% for the higher spikinglevel (20 mg·kg⁻¹). This precision reflects all of the errors in theoverall method, including the temperature fluctuations that occur duringSPME. The extraction efficiency, expressed as relative recoveries,varied from 78.5 to 122% at the lower spiking level and from 69.9 to106% at the higher spiking level. Under the extreme extractiontemperatures and times used in this study, the fiber lifetime dropped toapproximately 30 extractions before the extraction-to-extractionreproducibility decreased dramatically. Finally, the performance of theGC column comprised of the [C₁₂(BIM)₂] [NTf₂] IL stationary phase wasevaluated. A sample chromatogram of the six analytes separated on thisstationary phase is shown as supporting information. The reproducibilityof the analyte retention times during the study produced RSD valuesranging from 0.9 to 2.6% (n=60).

CONCLUSIONS

One of the most interesting and useful characteristics of ILs lies withtheir vast structural tunability which provides a wealth ofopportunities in adapting the physical and chemical properties of thematerial for applications in separation science. Herein, an analyticalmethod utilizing three distinct and separate IL components was used toperform high temperature headspace extraction and separation of sixanalytes possessing high boiling points and low vapor pressures. The[HMIM] [FAP] IL has been shown to be an excellent solvent in that thehydrophobic and refractory nature of the IL promotes dissolution of theapolar analytes while avoiding pressure build-up within the sample vialunder extreme temperatures. As a selective sorbent coating for SPME, thePIL component exhibits acceptable extraction efficiency of the studiedanalytes under the extreme experimental conditions. Finally, thestructural design of the IL-based GC stationary phase produces athermally stabile material that exhibits high separation selectivity ofthe analytes while producing minimal column bleed. The overall methodnicely demonstrates the versatility of ILs within separation science forthe determination of low volatility analytes using headspace extractionmode with detection limits ranging from 0.3 to 0.6 mg·kg⁻¹, relativerecoveries ranging from 69.9% to 106%, and precision values between 5.9and 22% as relative standard deviation. This method may be particularlyuseful for monitoring reaction products formed during catalysisexperiments when ILs are used as the reaction solvent. Future work willinvolve the use of blended ILs and task-specific ILs to further improvethe sensitivity and reproducibility of the overall method.

While the specification concludes with the claims particularly pointingout and distinctly claiming the invention, it is believed that thepresent invention will be better understood from the followingdescription. All percentages and ratios used herein are by weight of thetotal composition and normal pressure unless otherwise designated. Alltemperatures are in Degrees Celsius unless specified otherwise. Thepresent invention can comprise (open ended) or consist essentially ofthe components of the present invention as well as other ingredients orelements described herein. As used herein, “comprising” means theelements recited, or their equivalent in structure or function, plus anyother element or elements which are not recited. The terms “having” and“including” are also to be construed as open ended unless the contextsuggests otherwise. As used herein, “consisting essentially of” meansthat the invention may include ingredients in addition to those recitedin the claim, but only if the additional ingredients do not materiallyalter the basic and novel characteristics of the claimed invention.Preferably, such additives will not be present at all or only in traceamounts. However, it may be possible to include up to about 10% byweight of materials that could materially alter the basic and novelcharacteristics of the invention as long as the utility of the compounds(as opposed to the degree of utility) is maintained. All ranges recitedherein include the endpoints, including those that recite a range“between” two values. Terms such as “about,” “generally,”“substantially,” and the like are to be construed as modifying a term orvalue such that it is not an absolute, but does not read on the priorart. Such terms will be defined by the circumstances and the terms thatthey modify as those terms are understood by those of skill in the art.This includes, at very least, the degree of expected experimental error,technique error and instrument error for a given technique used tomeasure a value

Certain embodiments of the present invention are defined in the Examplesherein, in which all parts and percentages are by weight and degrees areCelsius, unless otherwise stated. It should be understood that theseExamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only. From the above discussion and theseExamples, one skilled in the art can ascertain the essentialcharacteristics of this invention, and without departing from the spiritand scope thereof, can make various changes and modifications of theinvention to adapt it to various usages and conditions. Allpublications, including patents and non-patent literature, referred toin this specification are expressly incorporated by reference herein.

While the invention has been described with reference to various andpreferred embodiments, it should be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the essential scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from the essential scope thereof.

Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed herein contemplated for carrying outthis invention, but that the invention will include all embodimentsfalling within the scope of the claims.

The publication and other material used herein to illuminate theinvention or provide additional details respecting the practice of theinvention, are incorporated be reference herein, and for convenience areprovided in the following bibliography.

Citation of the any of the documents recited herein is not intended asan admission that any of the foregoing is pertinent prior art. Allstatements as to the date or representation as to the contents of thesedocuments is based on the information available to the applicant anddoes not constitute any admission as to the correctness of the dates orcontents of these documents.

What is claimed is:
 1. A polymeric ionic liquid (PIL) comprising: i) acationic component comprising an ionic liquid (IL) that is polymerized,and ii) one or more anionic components, wherein the anionic componentscan be the same or different; wherein the anionic component comprises ataurate component.
 2. The PIL of claim 1, wherein the cationic componentcomprises least one or more: quaternary ammonium, protonated tertiaryamine, thionium, phosphonium, arsonium, carboxylate, sulfate orsulfonate groups which may be substituted or unsubstituted, saturated orunsaturated, linear, branched, cyclic, or aromatic.
 3. The PIL of claim1, wherein the cationic component comprises: a quaternary ammonium, aprotonated tertiary amine, imidazolium (IM) or substituted IM,pyrrolidinium or substituted pyrrolidinium, or pyridinium or substitutedpyridinium.
 4. The PIL of claim 1, wherein the cationic componentcomprises one or more of: monocationic components, dicationiccomponents, tricationic components, other multicationic components, andmixtures thereof.
 5. The PIL of claim 1, wherein the cationic componentcomprises an IL monomer modified through one or more of: incorporationof alkyl chains having different lengths, aromatic components, and/orhydroxyl-functionality.
 6. The PIL of claim 1, wherein the cationiccomponent is described by the general formula of (XRR′R″H)⁺, where X isN, P, or As; and wherein each of R, R′, R″ is selected from the groupconsisting of one or more of: a proton, an aliphatic group, a cyclicgroup, and an aromatic group.
 7. The PIL of claim 1, wherein thecationic component comprises one or more of: VHIM⁺, VDDIM⁺, VHDIM⁺, orBBIM⁺.
 8. A device comprising an absorbent or absorbent coatingcomprising at least one PIL of claim 1, coated onto a support.
 9. Thedevice of claim 8, wherein the support comprises one or more of: a solidfused silica support, a stir bar, a fiber, a film, a membrane, a fibrousmat, or a woven or non-woven material.
 10. The device of claim 8,wherein the PIL is at least partially crosslinked.
 11. A solid phasemicroextraction material (SPME) comprising an absorbent materialcomprising the PIL of claim
 1. 12. The solid phase microextractionmaterial of claim 11, wherein the support comprises one or more fibersat least partially coated with the PIL material.
 13. A solid phasemicroextraction (SPME) material comprising an absorbent materialcomprising a polymeric ionic liquid (PIL) material comprising a PIL,wherein the PIL comprises (i) a cationic component comprising an ionicliquid (IL) that is polymerized, and (ii) one or more anioniccomponents, wherein the anionic components can be the same or different;wherein the PIL material includes one or more extraction additives orphase modifiers that aid in selectively increasing the extractionefficiency or promoting wetting of glass or metal substrates, whereinthe extraction additives or phase modifiers comprise one or more of:micelles, monomer surfactants, cyclodextrins, nanoparticles, orsynthetic macrocycles.